Production method of a multilayer ceramic substrate

ABSTRACT

A multilayer ceramic substrate having a cavity is formed by the steps of laminating a plurality of ceramic green sheets including ceramic green sheets having through holes corresponding to the cavity to form a multilayer body, pressing the multilayer body and firing the pressed body. At this time, a shrinkage suppression green sheet is laminated on the surface of the a ceramic green sheet constituting the outermost layer of the multilayer body, and a shrinkage suppression green sheet piece is disposed on the ceramic green sheet exposed to the bottom of the cavity in accordance with the shape of the cavity. A burnable sheet is further disposed on the shrinkage suppression green sheet piece. Before the pressing step, an embedded green sheet separate from the ceramic green sheets (portion separated by inserting a cut) is disposed on the shrinkage suppression green sheet piece or the burnable sheet so that it is filled in the cavity. After the firing step, the embedded green sheet fired is removed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a production method of a multilayerceramic substrate having a cavity, particularly to an improvement in amethod for producing a multilayer ceramic substrate having a cavityutilizing a non-shrinkage firing process.

2. Description of the Prior Art

In the fields of electronics or other such devices, substrates formounting electronic devices thereon have been being widely used. Inrecent years, however, multilayer ceramic substrates have been proposedand put to practical use as substrates satisfying demands for reductionin size and weight and for multifunctionality and having highreliability. A multilayer ceramic substrate is constituted by aplurality of ceramic layers laminated, and integral incorporation of awiring conductor or an electronic device into each ceramic layer enablesa substrate to be highly dense.

With respect to the multilayer ceramic substrates, with an aim offacilitating miniaturization and reduction in height of electronics,multilayer ceramic substrates having a cavity (concave part) formedtherein for accommodating an electronic device have also been put topractical use. Since the multilayer ceramic substrate provided with acavity can be mounted as having an electronic device accommodated in thecavity, the aforementioned demands can satisfactorily be fulfilled,thereby making it possible to realize reduction in size and height ofthe multilayer ceramic substrate per se.

Incidentally, the multilayer ceramic substrate can be obtained throughthe steps of laminating a plurality of green sheets to form a multilayerbody and firing the multilayer body. The green sheet always shrinks asaccompanied by sintering in the firing step. This is a serious cause indecreasing the dimensional accuracy of the multilayer ceramic substrate.To be concrete, a shrinkage variation arises as accompanied by theshrinkage and, in the multilayer ceramic substrate being obtainedfinally, the dimensional accuracy falls around 0.5%.

Under these circumstances, a so-called non-shrinkage firing processcapable of suppressing the shrinkage in the in-plane direction andshrinking only in the thickness direction of the green sheets in thefiring step of the multilayer ceramic substrate was proposed (JP-A HEI10-75060, for example). As described in the prior art, when a multilayerbody of green sheets having attached thereto a sheet not shrinkable evenat the temperature in the aforementioned firing step is fired, theshrinkage in the in-plane direction is suppressed and only the shrinkagein the thickness direction is produced. According to this process, thedimensional accuracy in the in-plane direction of a multilayer ceramicsubstrate can be improved to fall around 0.05%.

When fabricating a multilayer ceramic substrate having the cavitymentioned above, even an application of the non-shrinkage firing processposes a problem of not always obtaining satisfactory dimensionalaccuracy or satisfactory flatness. This is because according to theordinary non-shrinkage firing process the binding force of shrinkagesuppression is not exerted onto the bottom of the cavity. When thebinding force of shrinkage suppression is not exerted onto the bottom ofthe cavity, flatness of the bottom required for mounting an electronicdevice thereon cannot be secured to the effect that there is apossibility of failing to mount the electronic device on the bottom.

In view of the above, an attempt to also attach a shrinkage-suppressingsheet onto the bottom of the cavity was made to eliminate thedisadvantage (JP-A 2003-318309, for example). The method of the priorart comprises the steps of forming on a carrier film ashrinkage-suppressing sheet containing an inorganic material forshrinkage suppression, inserting in the shrinkage-suppressing sheet acut of the shape corresponding to the contour of the bottom of thecavity, removing the portion of the sheet outside the cut, transferringthe shrinkage-suppressing sheet retained on the carrier sheet onto aceramic green sheet for a substrate (substrate ceramic green sheet) thatwill constitute the bottom of the cavity in the step of laminatingceramic green sheets for fabricating a crude multilayer body for thesubstrate and performing the firing step, with the shrinkage-suppressingsheet disposed on the bottom of the cavity. With this, it is madepossible to heighten the dimensional accuracy, difficult to formundesirable distortion within the cavity and possible to attain highdensity of wiring with high reliability.

However, only disposition of the shrinkage-suppressing sheet on theceramic green sheet for the substrate that will constitute the bottom ofthe cavity is difficult to completely eliminate the problem of thedeformation etc. of the cavity. Particularly, the method for producing amultilayer ceramic substrate requires a step of pressing a multilayerbody having a plurality of green sheets laminated and, in the pressingstep of the method for producing a multilayer ceramic substrate having acavity, there is a fair possibility of the cavity opening beingcollapsed and deformed in the pressing step. Also in the firing step, aphenomenon of rendering the periphery of the cavity opening to bulgewill occur, thus raising a possibility of the cavity opening beingdeformed.

As another method for fabricating a multilayer ceramic substrate havinga cavity, also conceivable is a method comprising the steps oflaminating a plurality of green sheets to form a multilayer body, firingthe multilayer body and subjecting the multilayer body to a boringprocess. However, since the sintered multilayer body is hard andfragile, a process with high accuracy is difficult to perform andexpensive equipment is required to use, leading to a high productioncost.

The present invention has been proposed in view of the conventionalstate of affairs, and the object thereof is to provide a method forproducing a multilayer ceramic substrate excellent in dimensionalaccuracy and flatness with ease at low cost and capable of eliminatinggeneration of the deformation etc. of the periphery of the cavity.

SUMMARY OF THE INVENTION

To attain the above object, the present invention provides a productionmethod of a multilayer ceramic substrate having a cavity, comprising thesteps of laminating a plurality of substrate green sheets includingcavity formation green sheets having through holes corresponding to thecavity to form a multilayer body, pressing the multilayer body andfiring the pressed body, the method further comprising the steps of,before the pressing step, laminating shrinkage suppression green sheetpieces on surfaces of the substrate green sheets, respectively, whichsurfaces constitute an outermost layer of the multilayer body,laminating a shrinkage suppression green sheet piece on a substrategreen sheet constituting a bottom of the cavity, disposing on theshrinkage suppression green sheet piece an embedded green sheet separatefrom the cavity formation green sheets to fill in the cavity and, afterthe firing step, removing the embedded green sheet fired.

In the above production method, since the non-shrinkage firing processis performed, with the shrinkage suppression green sheet disposed alsoon the substrate green sheets exposed to the bottom of the cavity, asdescribed above, the dimensional accuracy is secured and, also, theflatness of the cavity bottom is sufficiently secured. At the same time,the pressing step of the multilayer body is performed, with the embeddedgreen sheet disposed in the cavity, the pressing step is easy to performwith a flat mold die in the same manner as in the case of pressing amultilayer body having no cavity, and there is no possibility ofdeformation including cavity opening collapse and bulge of the peripheryof the cavity opening.

In the production method, the embedded green sheet is disposed on theshrinkage suppression green sheet piece and, at this time, when thebinding force of the shrinkage suppression green sheet is exerted on theembedded green sheet, there is a possibility of the stress accompaniedby the shrinkage of the embedded green sheet affecting the substrategreen sheet constituting the cavity bottom via the shrinkage suppressiongreen sheet. When there is a fear of the affection, it is preferred thatno binding force is exerted between the embedded green sheet and theshrinkage suppression green sheet piece.

To be specific, a sheet capable of being burnt down (burnable sheet) isinterposed between the shrinkage suppression green sheet piece and theembedded green sheet. In this case, the embedded green sheet is disposedvia the burnable sheet on the shrinkage suppression green sheet piece,and the burnable sheet is burnt down rapidly in the firing step.Therefore, no binding force of the shrinkage suppression sheet piece isexerted on the embedded green sheet and no shrinkage stress of theembedded green sheet affects the cavity bottom during the course offiring. In addition, the burnable sheet is burnt down in the firing stepand the fired embedded green sheet is rapidly removed.

In the present invention, the cavity bottom includes all surfacesexisting in the direction of the cavity depth. When the cavity forms amultistage, for example, the cavity bottom includes the bottom existingat the deepest position and the surfaces of steps existing at shallowerpositions. While the embedded green sheet has to be separate from thecavity formation green sheets, the separation in this case means boththat the cut pierces the cavity formation green sheet in its depthdirection and that the cut does not piece it.

On the other hand, in the multilayer ceramic substrate produced by theproduction method, the cavity assumes a specific shape different fromthe shape of a prior art cavity. The specific shape is prescribed by themultilayer ceramic substrate of the present invention. To be specific,the multilayer ceramic substrate of the present invention has aplurality of ceramic layers laminated and has a cavity, in which theopening area of the opening of the cavity is smaller than the openingarea of a portion at a position midway in the depth direction.

In the multilayer ceramic substrate of the present invention, the shapeof the cavity is advantageous in the case of sealing an electronicdevice within the cavity with a resin. In the multilayer ceramicsubstrates having a cavity, in many cases, an electronic device isaccommodated in the cavity and sealed with a resin. In this resin-seal,the problem will arise in that the resin sealed exfoliates and fallsoff, resulting from the difference in thermal expansion coefficientbetween the ceramic constituting the multilayer ceramic substrate andthe resin material used for the resin-seal. This problem becomesconspicuous particularly when a temperature change is repeated over along period of time. In the multilayer ceramic substrate of the presentinvention, since the opening area of the opening of the cavity issmaller than the opening area of the portion at a position midway in thedepth direction, as described above, the resin filled and hardened inthe cavity cannot pass through the cavity and is physically retainedwithin the cavity in an amassed state. Therefore, the sealed resin isprevented from exfoliating and falling off the ceramics. If the resinshould exfoliate, there is no case where the resin falls off the cavity.

In the multilayer ceramic substrate, generally, a conductive pattern isformed on the cavity bottom or inside the multilayer ceramic substrate.When the production of a multilayer ceramic substrate having aconductive pattern formed as straddling the periphery of the cavitybottom is to be attempted using the non-shrinkage firing process, with ashrinkage suppression green sheet piece disposed on the cavity pattern,a problem of disconnection of the conductive pattern, with the portionof contact with the sidewall of the cavity as a boundary, will possiblybe posed. This disconnection is caused by concentration of stress in theconductive pattern in contact with the lower end of the cavity sidewall(inner periphery of the cavity formation green sheet in contact with thecavity bottom formation green sheet) or in the cavity bottom formationceramic layer, which stress is generated by great shrinkage of, forexample, the cavity formation green sheet constituting the lower end inthe direction apart from the center of the cavity, because the bindingforce of the shrinkage suppression green sheet piece and shrinkagesuppression green sheet relative to the lower end of the cavity sidewallis small.

To eliminate the disadvantage, it is effective, in the portion on whicha conductive pattern is formed as straddling the periphery of the cavitybottom, that the end face of the shrinkage suppression green sheet pieceis disposed outside the end face of embedded green sheet to be laminatedthereon. This is prescribed by the second configuration of a multilayerceramic substrate according to the present invention, which has a cavityand comprises a plurality of ceramic layers integrally laminated andincluding a cavity bottom formation ceramic layer that constitutes abottom of the cavity and cavity formation ceramic layers, each of whichhas a through hole conforming to an opening of the cavity, and aconductive pattern formed on the cavity bottom formation ceramic layeras straddling a periphery of the cavity bottom, wherein in a portion ofthe periphery of the cavity bottom overlapping the conductive pattern, awall surface of the through hole of a first cavity formation ceramiclayer laminated immediately on the cavity bottom formation ceramic layeris at a position outside a wall surface of the through hole of a secondcavity formation ceramic layer laminated immediately on the first cavityformation ceramic layer.

A production method for producing the multilayer ceramic substrate ofthe second configuration further comprises, in addition to the steps inthe previous configuration, the steps of forming a conductive pattern onthe substrate green sheet constituting the bottom of the cavity asstraddling a periphery of the cavity bottom, forming a first cavityformation green sheet having a through hole in which a shrinkageprevention green sheet piece is embedded and a second cavity formationgreen sheet laminated immediately on the first cavity formation greensheet and having an embedded green sheet that is separate from thecavity formation green sheet embedded in the cavity, laminating thefirst and second cavity formation green sheets, respectively,immediately on the substrate formation green sheet constituting thebottom of the cavity and immediately on the first cavity formation greensheet so that the cavity bottom, the shrinkage suppression green sheetpiece and the embedded green sheet overlap to form the multilayer body,in which the shrinkage suppression green sheet piece in at least aportion of the periphery of the cavity bottom overlapping the conductivepattern has an end face disposed outside an end face of the embeddedgreen sheet the second cavity formation green sheet has.

With the above configuration, the shrinkage suppression green sheetpiece disposed on the cavity bottom comes into surface contact with theregion of the second cavity formation green sheet disposed immediatelythereon, which region constitutes the periphery of the cavity, therebyrestricting the shrinkage of the second cavity formation green sheet andthe cavity formation green sheet laminated thereon in the in-planedirection at the contact surface. Thus, since the stress exerted on theconductive pattern is dispersed, disconnection of the conductive patternon the cavity bottom is suppressed.

The residuals of the shrinkage suppression green sheet, shrinkagesuppression green sheet piece and embedded green sheet are removed fromthe fired multilayer body to obtain a multilayer ceramic substrate inwhich the wall surface of the through hole of the first cavity formationceramic layer laminated immediately on the bottom formation ceramiclayer is disposed outside the wall surface of the through hole of thesecond cavity formation ceramic layer, in at least the portion where theconductive pattern and the cavity bottom periphery overlap. In themultilayer ceramic substrate, disconnection of the conductive patternformed on the cavity bottom is prevented.

In the multilayer ceramic substrate of the second configuration, thecavity bottom includes all surfaces existing in the direction of thecavity depth. When the cavity forms a multistage, for example, thecavity bottom includes the bottom existing at the deepest position andthe surfaces of steps existing at shallower positions. While theembedded green sheet has to be separate from the cavity formation greensheets, the separation in this case means both that the cut pierces thecavity formation green sheet in its depth direction and that the cutdoes not piece it. Furthermore, the outside used in the presentinvention indicates the outside of the cavity of the multilayer ceramicsubstrate when seen from the top.

It is effective for solving the problem of disconnection to form on atleast the surface of the conductive pattern of the portionscorresponding to the periphery of the cavity bottom a softening layerthat gets soft at the firing temperature in the firing step. This isprescribed in the multilayer ceramic substrate of the thirdconfiguration of the present invention, which is produced through firingof a plurality of substrate green sheets laminated, having a cavity withan opening and comprises a plurality of ceramic layers including acavity bottom formation ceramic layer that constitutes a bottom of thecavity and integrally laminated, a conductive pattern formed on thecavity bottom formation ceramic layer as straddling a periphery of thecavity bottom and a softening layer that gets soft at a firingtemperature of the firing and is provided at least on a surface of theconductive pattern of a portion corresponding to the periphery of thebottom on the cavity bottom formation ceramic layer.

A production method for producing the multilayer ceramic substrate ofthe third configuration further comprises, in addition to the steps inthe previous configuration, the steps of forming a conductive pattern onthe substrate green sheet constituting the bottom of the cavity asstraddling a periphery of the cavity bottom and a softening layer thatgets soft at a firing temperature of the firing and is provided at leaston a surface of the conductive pattern of a portion corresponding to theperiphery of the bottom on the cavity bottom formation ceramic layer,before the pressing step, laminating the cavity formation green sheethaving the shrinkage suppression green sheet embedded in the throughhole immediately on the substrate formation green sheet constituting thecavity bottom so that the cavity bottom and the shrinkage suppressiongreen sheet piece overlap and laminating a cavity formation green sheetso that the embedded green sheet separate from each cavity formationgreen sheet as being filled in the cavity is disposed on the shrinkagesuppressing green sheet piece and, after the firing step, removing theembedded green sheet fired.

Also, in the multilayer ceramic substrate of the third configuration,since the non-shrinkage firing process is performed, with the shrinkagesuppression green sheet piece disposed also on the substrate green sheetexposed to the cavity bottom, the dimensional accuracy is secured, andthe flatness of the cavity bottom is also satisfactorily secured. At thesame time, since the multilayer body is pressed, with the embedded greensheet disposed in the cavity, the pressing step is easy to perform witha flat mold die in the same manner as in the case of pressing amultilayer body having no cavity, and there is no possibility ofdeformation including cavity opening collapse and bulge of the peripheryof the cavity opening.

Furthermore, since the softening layer is interposed between theconductive pattern and the lower end of the sidewall of the cavity, whenthe cavity formation green sheet constituting the lower end of thesidewall of the cavity shrinks in the direction apart from the center ofthe cavity in the firing step, the lower end of the sidewall of thecavity is moved as being slid on the surface of the softening layergetting soft. For this reason, the concentration of stress in theconductive pattern resulting from the shrinkage of the cavity formationgreen sheet in the in-plane direction is alleviated by means of thesoftening layer to suppress disconnection of the conductive pattern onthe cavity bottom.

The residuals of the shrinkage suppression green sheet, shrinkagesuppression green sheet piece and embedded green sheet are removed fromthe fired multilayer body to obtain a multilayer ceramic substratehaving the softening layer on at least the conducting pattern of theportions corresponding to the periphery of the cavity and giving rise tono disconnection of the conductive pattern on the cavity bottom.

Incidentally, also in the multilayer ceramic substrate of the thirdconfiguration, the cavity bottom includes all surfaces existing in thedirection of the cavity depth. When the cavity forms a multistage, forexample, the cavity bottom includes the bottom existing at the deepestposition and the surfaces of steps existing at shallower positions.While the embedded green sheet has to be separate from the cavitysidewall formation green sheets, the separation in this case means boththat the cut pierces the cavity formation green sheet in its depthdirection and that the cut does not piece it.

According to the production method of the present invention, it ispossible to produce a multilayer ceramic substrate having a cavityexcellent in dimensional accuracy and flatness without any deformationincluding cavity opening collapse and bulge around the cavity opening.Also in the production method of the present invention does not requireeither adoption of a boring process after sintering or use of specialequipment for the boring process, thus making it possible to produce themultilayer ceramic substrate with ease and at low cost.

Even when the multilayer ceramic substrate having an electronic deviceaccommodated in the cavity and sealed with a resin, for example, hasundergone thermal stress a great number of times over a long period oftime, the resin would not exfoliate and fall off. Thus, it is possibleto materialize a multilayer ceramic substrate with high reliability.

Moreover, according to the multilayer ceramic substrates and theproduction methods thereof having the second and third configurations,in addition to the aforementioned effects, it is possible to providemultilayer ceramic substrates elimination disconnection of theconductive pattern resulting from the shrinkage of the region around thecavity in the in-plane direction.

The above and other objects, characteristic features and advantages ofthe present invention will become apparent to those skilled in the artfrom the description to be made herein below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross section of the principal part showing oneexample of a multilayer ceramic substrate to be produced.

FIG. 2 is a flowchart showing the production process in the firstembodiment of the present invention.

FIG. 3( a) is a schematic side view of a ceramic green sheet and FIG. 3(b) a schematic side view of a shrinkage suppression green sheet.

FIG. 4( a) is a schematic plan view of a first composite green sheet andFIG. 4( b) a schematic plan view of a composite green sheet forming anoutermost layer.

FIG. 5 is a schematic plan view of a cut formation sheet.

FIG. 6 is a schematic cross section of the principal part showing theproduction process for the multilayer ceramic substrate in the firstembodiment, FIG. 6( a) showing a laminating step, FIG. 6( b) a firingstep, FIG. 6( c) a cavity formation step and FIG. 6( d) a shrinkagesuppression sheet removal step.

FIG. 7 is a schematic cross section showing the state in which anelectronic device is mounted on the multilayer ceramic substrateproduced in the first embodiment.

FIG. 8 is a typical view showing one example of the shape of the cavityof a multilayer ceramic substrate.

FIG. 9 is a schematic view showing the state in which the electronicdevice is sealed with a resin.

FIG. 10( a) is a schematic plan view showing a second composite greensheet produced in the second embodiment of the present invention andFIG. 10( b) a schematic plan view of a second cut formation sheet.

FIG. 11 is a schematic cross section of the principal part showing anexample of the production process of a multilayer ceramic substratehaving a cavity of a two-step structure in the second embodiment, FIG.11( a) showing a laminating step, FIG. 11( b) a firing step and FIG. 11(c) a multilayer ceramic substrate.

FIG. 12 is a schematic cross section showing the state in which anelectronic device is mounted onto the multilayer ceramic substrateproduced in the second embodiment.

FIG. 13 is a typical view showing one example of the cavity shape of amultilayer ceramic substrate having a multistage cavity.

FIG. 14 is a typical view showing another example of the cavity shape ofa multilayer ceramic substrate having a multistage cavity.

FIG. 15 is a schematic cross section of the principal part showing thedeformation of a cavity bottom portion of a multilayer ceramicsubstrate.

FIG. 16 is a schematic cross section of the principal part showing anexample of the configuration of a multilayer body according to the thirdembodiment of the present invention.

FIG. 17 is schematic cross section of the principal part showing anotherexample of the configuration of a multilayer body according to the thirdembodiment.

FIG. 18 is a schematic cross section of the principal part showing theproduction process of a multilayer ceramic substrate according to thefourth embodiment of the present invention, FIG. 18( a) showing alaminating step, FIG. 18( b) a firing step, FIG. 18( c) a step ofremoving the fired embedded green sheet and FIG. 18( d) a completedmultilayer ceramic substrate.

FIG. 19 is a schematic perspective view showing a step of applying ashrinkage suppression green sheet piece and a burnable sheet piece to aceramic green sheet.

FIG. 20 is a schematic cross section of the principal part showing anexample of the production process of a multilayer ceramic substratehaving a cavity of a two-step structure according to the fifthembodiment of the present invention, FIG. 20( a) showing a laminatingstep, FIG. 20( b) a firing step and FIG. 20( c) a multilayer ceramicsubstrate.

FIG. 21( a) is a plan view of the principal part showing one example ofa multilayer ceramic substrate according to the sixth embodiment of thepresent invention, FIG. 21( b) an enlarged plan view of the principalpart in FIG. 21( a), FIG. 21( c) a cross section taken along lineXXI(a)-XXI(a) and FIG. 21( d) an enlarged cross section of the principalpart in FIG. 21( c).

FIG. 22 is a view showing in detail the cavity shape of the multilayerceramic substrate shown in FIG. 21.

FIG. 23 is a schematic cross section showing the state in which anelectronic device is sealed within the cavity with a resin.

FIG. 24( a) is a schematic side view of a ceramic green sheet and FIG.24( b) a schematic side view of a shrinkage suppression green sheet.

FIG. 25( a) is a schematic plan view of a first composite green sheetand FIG. 25( b) a schematic plan view of a composite green sheet formingan outermost layer.

FIG. 26 is a schematic plan view of a cut formation sheet.

FIG. 27 is a schematic plan view of a cavity bottom formation greensheet.

FIG. 28 is a schematic cross section of the principal part of aproduction process of a multilayer ceramic substrate according to thesixth embodiment of the present invention, FIG. 28( a) showing alaminating step, FIG. 28( b) a firing step, FIG. 28( c) a cavityformation step and FIG. 28( d) a shrinkage suppression sheet removalstep.

FIG. 29 is a schematic cross section of the principal part showing alaminating step in the production process of a multilayer ceramicsubstrate when a shrinkage suppression sheet piece and an embedded greensheet have substantially the same shape.

FIG. 30 is a schematic cross section showing the state in which anelectronic device is mounted onto the multilayer ceramic substrateproduced in the sixth embodiment.

FIG. 31 is a schematic plan view showing one example of a multilayerceramic substrate according to the seventh embodiment of the presentinvention.

FIG. 32 is a schematic plan view showing another example of themultilayer ceramic substrate according to the seventh embodiment.

FIG. 33 is a schematic plan view showing still another example of themultilayer ceramic substrate according to the seventh embodiment.

FIG. 34 is a schematic cross section of the principal part showing oneexample of a multilayer ceramic substrate having a cavity of amultistage structure according to the eighth embodiment of the presentinvention.

FIG. 35 is a view showing one example of the cavity shape of amultilayer ceramic substrate having a multistage cavity.

FIG. 36 is a view showing another example of the cavity shape of amultilayer ceramic substrate having a multistage cavity.

FIG. 37( a) is a schematic plan view of a second composite green sheetproduced in the eighth embodiment and FIG. 37( b) a schematic plan viewof a second cut formation sheet.

FIG. 38 is a schematic plan view of a second cavity bottom formationgreen sheet.

FIG. 39 is a schematic cross section of the principal part showing anexample of a production process of a multilayer ceramic substrate havinga cavity of a two-step structure according to the eighth embodiment.

FIG. 40 is a schematic cross section showing the state in which anelectronic device is mounted onto a multilayer ceramic substrateproduced in the eighth embodiment.

FIG. 41 is a schematic cross section of the principal part showing thedeformation of a cavity bottom portion of a multilayer ceramicsubstrate.

FIG. 42 is a schematic cross section of the principal part showing oneexample of a multilayer body according to the ninth embodiment of thepresent invention.

FIG. 43 is a schematic cross section of the principal part showinganother example of the configuration of a multilayer body according tothe ninth embodiment.

FIG. 44 is a schematic cross section of the principal part showing aproduction process of a multilayer ceramic substrate according to thetenth embodiment of the present invention, FIG. 44( a) showing alaminating step, FIG. 44( b) a firing step, FIG. 44( c) a step ofremoving the fired embedded green sheet and FIG. 44( d) a completedmultilayer ceramic substrate.

FIG. 45 is a schematic perspective view showing a step of applying aceramic green sheet piece and a burnable sheet piece to a ceramic greensheet.

FIG. 46 is a schematic cross section of the principal part of aproduction process of a multilayer ceramic substrate having a cavity ofa two-step structure according to the eleventh embodiment of the presentinvention, FIG. 46( a) showing a laminating step, FIG. 46( b) a firingstep and FIG. 46( c) a multilayer ceramic substrate.

FIG. 47( a) is a schematic plan view showing one example of a multilayerceramic substrate according to the twelfth embodiment of the presentinvention. FIG. 47( b) is a sectional view of the main part of FIG. 47(a) taken along line XLVII(b)-XLVII(b) in FIG. 47( a).

FIG. 48 is a schematic cross section of the principal part showing alaminating step of the multilayer ceramic substrate according to thetwelfth embodiment.

FIG. 49( a) is a schematic plan view showing one example of a multilayerceramic substrate according to the thirteenth embodiment of the presentinvention, FIG. 49( b) an enlarged plan view of the principal part inFIG. 49( a), FIG. 49( c) a schematic cross section of the principal parttaken along line XLIX(a)-XLIX(a) in FIG. 49( a) and FIG. 49( d) anenlarged cross section of the principal part in FIG. 49( c).

FIG. 50 is a view showing in detail the cavity shape of the multilayerceramic substrate shown in FIG. 49.

FIG. 51 is a schematic cross section showing the state in which anelectronic device is sealed within the cavity with a resin.

FIG. 52( a) is a schematic side view of a ceramic green sheet and FIG.52( b) a schematic side view of a shrinkage suppression green sheet.

FIG. 53( a) is a schematic plan view of a first composite green sheetand FIG. 53( b) a schematic plan view of a composite green sheet formingan outermost layer.

FIG. 54 is a schematic plan view of a cut formation sheet.

FIG. 55 is a schematic plan view of a cavity bottom formation greensheet.

FIG. 56 is a schematic cross section of the principal part of aproduction process of a multilayer ceramic substrate according to thethirteenth embodiment of the present invention, FIG. 56( a) showing alaminating step, FIG. 56( b) a firing step, FIG. 56( c) a cavityformation step and FIG. 56( d) a shrinkage suppression sheet removalstep.

FIG. 57 is a schematic cross section showing the state in which anelectronic device is mounted onto the multilayer ceramic substrateproduced in the thirteenth embodiment.

FIG. 58 is a schematic plan view showing one example of a multilayerceramic substrate according to the fourteenth embodiment of the presentinvention.

FIG. 59 is a schematic plan view showing another example of themultilayer ceramic substrate according to the fourteenth embodiment.

FIG. 60 is a schematic cross section showing still another example ofthe multilayer ceramic substrate according to the fourteenth embodiment.

FIG. 61 is a schematic cross section showing one example of a multilayerceramic substrate having a cavity of a multistage structure according tothe fifteenth embodiment of the present invention.

FIG. 62 is a view showing one example of the cavity shape of themultilayer ceramic substrate having the cavity of the multistagestructure.

FIG. 63 is a view showing another example of the cavity shape of themultilayer ceramic substrate having the cavity of the multistagestructure.

FIG. 64( a) is a schematic plan view of a second composite green sheetproduced in the fifteenth embodiment and FIG. 64( b) a schematic planview of a second cut formation sheet.

FIG. 65 is a schematic plan view of a second cavity bottom formationgreen sheet.

FIG. 66 is a schematic cross section of the principal part showing theproduction process of the multilayer ceramic substrate produced in thefifteenth embodiment, FIG. 66( a) showing a laminating step and FIG. 66(b) a firing step.

FIG. 67 is a schematic cross section showing the state in which anelectronic device is mounted onto the multilayer ceramic substrateproduced in the fifteenth embodiment.

FIG. 68 is a schematic cross section of the principal part showing thedeformation of the cavity bottom portion of the multilayer ceramicsubstrate.

FIG. 69 is a schematic cross section of the principal part showing oneexample of a multilayer body according to the sixteenth embodiment ofthe present invention.

FIG. 70 is a schematic cross section of the principal part showinganother example of the configuration of the multilayer body according tothe sixteenth embodiment.

FIG. 71 is a schematic cross section of the principal part showing aproduction process of a multilayer ceramic substrate according to theseventeenth embodiment of the present invention.

FIG. 72 is a schematic perspective view showing a step of applying ashrinkage suppression green sheet piece and a burnable sheet piece to aceramic green sheet.

FIG. 73 is a schematic cross section of the principal part showing aproduction process of a multilayer ceramic substrate having a cavity ofa two-step structure according to the eighteenth embodiment of thepresent invention, FIG. 73( a) showing a laminating step, FIG. 73( b) afiring step and FIG. 73( c) a multilayer ceramic substrate.

FIG. 74 is a drawing-alternative picture showing a cavity shape of themultilayer ceramic substrate produced in Example 1.

FIG. 75 is a drawing-alternative picture showing a cavity shape of themultilayer ceramic substrate produced in Example 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A production method of a multilayer ceramic substrate and a multilayerceramic substrate produced by the production method and provided with acavity of a specific shape according to the present invention will bedescribed in detail herein below with reference to the accompanyingdrawings.

A multilayer ceramic substrate to be produced in the first embodimentwill be described. It has a cavity (concave) for accommodating anelectronic device or other such device.

FIG. 1 shows an example of the simplest model for a multilayer ceramicsubstrate 1 having a cavity. In this example, plural (nine here) ceramiclayers 2 to 10 are laminated and made integral. Of these ceramic layers2 to 10, two lower ceramic layers 2 and 3 are formed with no throughhole for formation of a cavity and are flat ceramic layers. Of the two,the upper ceramic layer 3 has an upper surface 3 a, part of which isexposed to a cavity to constitute the cavity bottom.

On the other hand, the remaining ceramic layers 4 to 10 laminated on theceramic layer 3 are formed respectively with through holes correspondingto a cavity 11. These through holes are connected contiguously to formthe cavity 11 as the prescribed space. The shape of the cavity openingis a square, for example, but may optionally be changed to a rectangle,an oval, etc. When a square or rectangular cavity is adopted, however,the angular corners thereof are preferably rounded into circular arcs.With this, otherwise generated stress can be alleviated, and otherwiseformed cracks can be eliminated. When adopting the non-shrinkage firingprocess using a shrinkage suppression sheet with respect to the cavitywith angular corners, the side walls of the cavity 11 are attractedoutward to concentrate the stress in the angular corners, therebypossibly forming cracks. By rounding the angular corners into circulararcs, it is possible to alleviate the stress concentration and preventthe crack formation. The curvature radius R in the circular arc in thiscase is preferred to be 0.05 mm or more. It is more preferable to setthe curvature radius R depending on the thickness of a shrinkagesuppression sheet. It was experimentally confirmed that no crack wasformed when the curvature radius was 0.1 mm or more relative to a 75μm-thick shrinkage suppression sheet and when the curvature radius was0.51 mm relative to a 250 μm-thick shrinkage suppression sheet. Thoughnot shown in the drawings, provision of a conductive pattern formounting an electronic device mounted thereon on the bottom of thecavity 11 is generally put into practice. There is a case where viaholes for heat radiation are formed in the cavity bottom.

The multilayer ceramic substrate 1 having the cavity 11 is fabricatedthrough a method comprising the steps of laminating plural green sheets,pressing the laminated sheets to form a multilayer body and firing themultilayer body. In order to secure the dimensional accuracy, it isnecessary to suppress shrinkage during the firing step. This is stillunsatisfactory and, it is further necessary to eliminate deformationincluding collapse of the opening of the cavity 11 and bulges around theopening of the cavity 11 that is made during the pressing step.

In view of the above, the present embodiment adopts the non-shrinkagefiring process and performs the pressing and firing steps, with a sheetfor being embedded (embedded sheet) disposed in the space correspondingto the cavity, to facilitate the elimination of collapse during thepressing step. A production method of the multilayer ceramic substrateof the present embodiment will be described.

A step flowchart of the production method of this embodiment is shown inFIG. 2. The production method fundamentally comprises a multilayer bodyformation step (S1), a firing step (S2) and a cavity formation step(S3). It may further comprise a shrinkage suppression sheet removal step(S4). The multilayer body formation step (S1) comprises a green sheetformation step (S11), a composite green sheet formation step (S12), acut formation step (S13), a via hole formation step (S14), aconductor-printing step (S15), a laminating step (S16) and a pressingstep (S17).

Each step will be described. To fabricate the multilayer ceramicsubstrate, the green sheet formation step (S11) that is the initial stepin the multilayer body formation step (S1) is first performed. In thegreen sheet formation step (S11), a ceramic green sheet (correspondingto a green sheet for a substrate) 21 shown in a FIG. 3( a) and ashrinkage suppression green sheet 22 shown in FIG. 3( b) are formed.Each of the ceramic green sheet 21 and shrinkage suppression green sheet22 are generally formed on a plastic sheet as a support 23 in the stateof intimate contact with the surface of the plastic sheet. While theplastic sheet used as the support 23 is arbitral insofar as the surfacethereof is flat and smooth. For example, a sheet of PolyethyleneTelephthalate (PET) is preferably usable. The thickness of the support23 is preferred to be not deformed during the step and be easy tohandle. It is generally in the range of 50 to 150 μm.

As the production method of the ceramic green sheet 21, a methodcomprising mixing ceramic powder with an organic vehicle to prepareslurry (dielectric paste) and forming the slurry on the support 23(resin sheet of PET) in the form of a film by a sheet formation method,such as the doctor blade method can be cited. When the multilayerceramic substrate is intended to form a glass ceramic substrate, slurryhaving glass powder in addition to the ceramic power mixed therewith maybe used.

Incidentally, the organic vehicle is a product having a binder dissolvedin an organic solvent and is composed preponderantly of a solventincluding terpineol, butylcarbitol, acetone, toluene, isopropyl alcohol,etc., a binder including ethylcellulose, polyvinyl butyral, etc. and aplasticizer including di-n-butylphthalate, etc. The content of theorganic vehicle is not particularly limited, but an ordinary contentcomprises 1 to 5 mass % of a binder and 10 to 50 mass % of a solvent,for example.

The dielectric paste may be in the form of an organic paint containingthe organic vehicle or a water-soluble paint having a water-solublebinder, dispersant, etc. dissolved in water. Here, the water-solublebinder is not particularly limited and may appropriately be selectedfrom among polyvinyl alcohol, cellulose, water-soluble acrylic resin,emulsion, etc.

As described above, the dielectric paste contains ceramic powderconstituted by a dielectric porcelain composition, the composition ofwhich is arbitrarily determined. Therefore, in preparing the ceramicpowder, raw materials (chief ingredients and accessory ingredients) areselected depending on the composition of the dielectric porcelaincomposition. In this case, modes of the chief ingredients and accessoryingredients that are the raw materials are not particularly limitative.As the chief ingredients and accessory ingredients that are the rawmaterials, oxides and compounds enabled by firing to be oxides can beused. As the compounds enabled by firing to be oxides, carbonates,nitrates, oxalates and organic metal compounds can be cited. Of course,an oxide and a compound enabled by firing to be an oxide may be usedtogether. The contents of the ingredients in the raw materials may bedetermined so as to acquire the composition of the dielectric porcelaincomposition after the ingredients are fired. A ceramic powder productionmethod is arbitrarily selected. Powder obtained from either theliquid-phase synthesis or the solid-phase method; for example, may beavailable.

When fabricating a glass ceramic substrate that is a Low TemperatureCofired Ceramic (LTCC) substrate, as described above, ceramic powder(ceramic ingredients) and glass powder (glass ingredients) are usedtogether. At this time, these ceramic ingredients and glass ingredientsmay appropriately be selected based on the relative permittivity andfiring temperature aimed at. To be specific, a combination of aluminaenabled by firing at 1000° C. or less to be a glass ceramic substrate(ceramic ingredient: crystal phase) and silicon oxide (glass ingredient:glass phase) can be cited. Other ceramic ingredients include magnesia,spinel, silica, mulite, mullite, forsterite, steatite, cordierite,strontium, feldspar, quartz, zinc silicate, zirconia and titania. As theglass ingredient, borosilicate glass, barium borosilicate glass,strontium borosilicate glass, zinc borosilicate glass, potassiumborosilicate glass can be cited. The glass ceramic substrate preferablycomprises 60 to 80% by volume of the glass ingredient and 40 to 20% byvolume of the ceramic ingredient that is an aggregate. When the glassingredient falls outside the above range, a composite composition isdifficult to form because the strength and sintering property arelowered.

While the shrinkage suppression green sheet 22 is produced fundamentallyin the same manner as in the production method of the ceramic greensheet 21, the two sheets differ in ingredient. That is to say, theshrinkage suppression green sheet 22 is formed of a shrinkagesuppression material difficult to shrink at the temperature at which theceramic green sheet is fired and is a green sheet having its shrinkagesuppressed. As the shrinkage suppression material, a compositioncontaining at least one species of quartz, cristobalite and tridymite isusable. Otherwise, a composition containing alumina is available.

Since no part or only part of these shrinkage suppression materials issintered at the firing temperature of the ceramic and glass ingredientscontained in the ceramic green sheet 21, the materials do not initiateshrinking at the firing temperature of the ceramic green sheet 21.Therefore, when the shrinkage suppression green sheet 22 formed of theshrinkage suppressing material is laminated on the ceramic green sheet21 in an intimate contact state, it functions to suppress shrinkage ofthe ceramic green sheet 21 in the plane surface direction during thecourse of firing.

Incidentally, in forming the shrinkage suppression green sheet 22, theshrinkage suppression material (composition containing at least onespecies of quartz, cristobalite and tridymite) may be added withsintering aids. Also in this case, the same effect can be obtained.Though the sintering aids are sintered at the firing temperature of theceramic or glass ingredient, since the thermal expansion coefficients ofquartz, cristobalite and tridymite that are the shrinkage suppressionmaterials are 20 ppm/° C., 50 ppm/° C. and 40 ppm/° C., respectively,that are larger than that of the ceramic or glass ingredient, even whenthe sintering aids have shrunk after firing, the dimensional changesbefore and after the firing are cancelled each other to make it possibleto suppress the ceramic green sheet from shrinking.

As the sintering aids to be used, oxides being softened or forming aliquid phase at the sintering initiating temperature of the ceramic orglass ingredient or less can be cited. In the former oxides, the softensintering aids allow grains of the shrinkage suppression material to bejoined and are consequently sintered. In the latter oxides, the producedliquid phase allows the grains surfaces of the shrinkage suppressionmaterial to react with each other, resulting in the grains being joinedand are consequently sintered. While the oxides to be used as thesintering aids are not particularly limited, examples thereof includealuminum lead silicate glass, alkali lead silicate glass, alkaline earthlead silicate glass, lead borosilicate glass, alkali borosilicate glass,alkaline earth lead aluminum borate glass, aluminum lead borate glass,alkaline earth lead borate glass and zinc lead borate glass. One or moreof these may be selected and used.

Alkali metal compounds can also be used as the sintering aids. Thealkali metal compounds have an effect of facilitating the progress ofsintering SiO₂. Accordingly, when adding an alkali metal compound to acomposition containing at least one species of quartz, cristobalite andtridymite, the shrinkage suppression green sheet 22 is slightly sinteredwith the sintering of the ceramic green sheet 21. While the alkali metalcompounds are not particularly limited, lithium carbonate, potassiumcarbonate, sodium carbonate, lithium oxide and potassium oxide, forexample, can be cited.

Furthermore, as the material used for the shrinkage suppression greensheet 22, a composition containing tridymite and an oxide difficult tosinter can also be used. The tridymite is a material enabling thesintering temperature to be variously changed depending on the selectionof a composition. However, the thermal expansion coefficient oftridymite is large and reaches 40 ppm/° C. depending on the temperature.For this reason, there is a possibility of tridymite exfoliating beforethe ceramic green sheet 21 being sintered due to an unduly difference inthermal expansion coefficient from the ceramic green sheet 21 (about 3to 10 ppm/° C.), for example. In order to prevent this from occurring,therefore, an oxide not sintered at the firing temperature of theceramic green sheet 21 is added to the tridymite to adjust the thermalexpansion coefficient, thereby suppressing the composition fromexfoliating before the ceramic green sheet 21 being sintered. While theoxides not sintered during the course of firing of the ceramic greensheet 21 are not particularly limited, quartz, molten quartz, alumina,mullite and zirconia, for example, can be cited.

The ceramic green sheet 21 and shrinkage suppression green sheet 22 arefabricated as described above. The thickness of each sheet is preferablyin the range of around 20 μm to 300 μm in consideration of formation ofa via electrode and an internal electrode described later.

In a composite green sheet formation step (S12) after the fabrication ofthe ceramic green sheet 21 and shrinkage suppression green sheet 22, acomposite green sheet (green sheet combining the ceramic green sheetwith the shrinkage suppression green sheet) is fabricated utilizing thedescription described above. The composite green sheet fabricated herecomprises a first composite green sheet laminated immediately on thesubstrate green sheet (ceramic green sheet) constituting the cavitybottom and an uppermost composite green sheet laminated as an uppermostcomposite shrinkage suppression green sheet.

A first composite green sheet 26 shown in FIG. 4( a) is produced. First,the ceramic green sheet 21 produced in the green sheet formation step(S11) is formed with a first through hole 24. The first through hole 24may be formed by punching out a predetermined portion of the ceramicgreen sheet 21, with the ceramic green sheet in intimate contact withthe surface of a support 23, with a die of a puncher or using a laserbeam or with a microdrill or by punching. The first through hole isformed to correspond to the shape of the cavity, and the shape thereofis not particularly restricted, but may be square, rectangular orcircular.

The shrinkage suppression sheet 22 produced in the green sheet formationstep (S11) is placed on a support 23 and cut into the same shape as thefirst through hole to obtain a first fitting sheet 25 (corresponding tothe shrinkage suppression green sheet piece). The cut first fittingsheet 25 is fitted in the first through hole 24 to form a firstcomposite green sheet 26. At this time, in order to make the firstcomposite green sheet 26 flat, preferably, the thickness of the ceramicgreen sheet 21 is the same as that of the first fitting sheet 25.

An uppermost composite green sheet 29 is produced in accordance with thesame production method as that of the first composite green sheet 26. Inthe uppermost composite green sheet 29, as shown in FIG. 4( b), theshrinkage suppression green sheet 22 is formed with a through hole inwhich a ceramic green sheet piece is fitted. To be specific, theshrinkage suppression green sheet produced in the green sheet formationstep (S11) is formed with a second through hole 27 corresponding to theopening of the cavity. The production method of the second through hole27 is the same as that of the first through hole 24. The ceramic greensheet 21 produced in the green sheet formation step (S11) is placed on asupport 23 and cut into the same shape as the second through hole 27 toobtain a second fitting sheet 28. The cut second fitting sheet 28 isfitted in the second through hole 27, and the resultant composite sheetis allowed to exfoliate from the support 23 to form an uppermostcomposite green sheet 29. Also in this case, in order to make theuppermost composite green sheet 29 flat, preferably, the thickness ofthe shrinkage suppression green sheet 22 is the same as that of thesecond fitting sheet 28.

In the cut formation step (S13), the ceramic green sheet 21 is formedwith a cut to be used as a cavity formation green sheet. Specifically,in the cut formation step (S13), the ceramic green sheet 21 produced inthe green sheet formation step (S11) is formed with a cut (or adiscontinuous portion) 31 to form a cut formation sheet 30 as shown inFIG. 5. The cut 31 indicates the discontinuous portion pierced in thedirection of the thickness of the ceramic green sheet 21. Incidentally,the discontinuous portion includes what is not pierced in the sheetwidth direction. The cut 31 is formed at the same position and in thesame shape as the first through hole 24 to overlap the first throughhole 24 when the cut formation sheet 30 overlaps the previously producedfirst composite green sheet 26. The cut 31 may be formed by punching outa predetermined portion of the ceramic green sheet 21, with the ceramicgreen sheet 21 in intimate contact with the surface of the support 23,with a die of a puncher or using a laser beam or with a microdrill or bypunching.

In the cut formation step (S13), the cut may be inserted into theceramic green sheets 21 one by one or together in a lump. In eithercase, in the cut formation sheets 30, the portions 30 a separated by thecuts 31 are left intact and utilized as embedded green sheets in thelaminating and firing steps.

The first composite green sheet 26, cut formation sheets 30 and ceramicgreen sheet constituting the bottom of the cavity that are ceramic greensheet constituting the ceramic layers of a multilayer ceramic substrateafter being fired (hereinafter referred to collectively as “dielectriclayer sheets”) are provided with a via hole, via electrode, internalelectrode pattern, etc.

In the via hole formation step (S14), for example, a via hole forforming a via electrode therein is formed using a laser beam or amicrodrill or by punching. When the dielectric layer sheet is irradiatedwith a laser beam, the ceramic powder and binder resin are sublimed toform a hole. The laser to be used advantageously is a short-wavelengthUV-YAG laser or excimer laser. Use of a laser beam enables the diameterof the via hole to be 100 μm or less with ease. On the other hand, whileit is difficult to make the diameter of the via hole small with amicrodrill or by punching, compared with the use of a laser beam, thereis a merit in that the processing can be performed at low cost. At anyrate, conductor paste is filled in the via hole thus formed by thesetechniques to form a minute via electrode with high precision.

In the conductor-printing step (S15), conductor paste is filled in thevia hole formed in the via hole formation step (S14) to form a viaelectrode. The conductor paste contains metal or alloy powder of copper,silver, silver-palladium, palladium, nickel, etc. and is adjusted tohave viscosity having prescribed flowability. Also in theconductor-printing step (S15), an internal electrode pattern is printedon the surface of the dielectric layer sheet in a prescribed pattern.Paste for the internal pattern, similarly to the conductive paste,contains metal or alloy powder of copper, silver, silver-palladium,palladium, nickel, etc. and is adjusted to have viscosity havingprescribed flowability. The internal electrode paste and via electrodepaste may be formed of different materials.

Since the material constituting the dielectric layer sheet has areduction resistant property and since inexpensive base metal can beused as the conductive material, nickel or nickel alloy may be used asthe conductive material. As the nickel alloy, alloy of nickel and one ormore elements selected from the group consisting of manganese, chromium,cobalt and aluminum is preferred. The content of nickel in the alloy ispreferably 95 mass % or more. The via electrode and internal electrodepattern may contain minute various ingredients, such as phosphorus (P),in an amount of around 0.1 mass % or less. The thickness of the internalelectrode pattern is appropriately determined depending on theapplication thereof and is preferably around 1 μm to 15 μm, morepreferably around 2.5 μm to 10 μm.

The via electrode paste or internal electrode paste is produced throughkneading with a vehicle similar to that of the conductive paste. Thecontent of the vehicle in the via electrode paste or internal electrodepaste is adjusted similarly in the case of the conductive paste. The viaelectrode paste or internal electrode paste may be added with additives,such as dispersants, plasticizers, dielectric materials, insulatingmaterials, etc. as occasion demands. The amount of the additives ispreferred to be 10 mass % or less in total.

Subsequently, the via electrode paste or internal electrode paste isprinted on the dielectric layer sheet to form a via electrode orinternal electrode pattern. The via electrode paste is filled andsolidified by the stopgap printing, for example, to form a viaelectrode. The internal electrode paste is applied onto the ceramicgreen sheet, for example, in a prescribed pattern by the screen printingto form an internal electrode pattern.

After the via electrode or internal electrode pattern is formed on eachdielectric layer sheet, the thus fabricated sheets are laminated in thelaminating step (S16) to form a multilayer body 32. The configuration ofthe multilayer body 32 from the laminating step (S16) to the shrinkagesuppression sheet removal step (S4) is shown in FIG. 6( a) to FIG. 6(d). Incidentally, the step shown in FIG. 6( c) and the step shown inFIG. 6( d) may be performed inversely or simultaneously.

In the laminating step (S16), as shown in FIG. 6( a), a shrinkagesuppression green sheet 22, ceramic green sheet 21, first compositegreen sheet 26, cut formation sheet 30 and uppermost composite greensheet 29 are laminated in the order mentioned from the lowermost layer.The number of each sheet may be singular or plural. In the exampleshown, laminated on the lowermost sheet are two ceramic green sheets 21on which a first composite green sheet 26 and six cut formation sheets30 are laminated to configure a multilayer body 32. Therefore, the ninelayers constitute the substrate green sheet, and the first compositegreen sheet 26 and six cut formation sheets 30 constitute the cavityformation green sheet. The configuration of the multilayer body 32 maybe an upside-down configuration or a configuration having the sameconfiguration added across the shrinkage suppression green sheet 22.

When laminating two or more cut formation sheets 30, for example, thesemay be formed of the same material or differ materials. In the lattercase, however, they are preferred to be substantially the same incompressibility at the time of pressing and in degree of shrinkage andthermal expansion coefficient at the time of firing. By so doing, warpof the substrate resulting from the difference in compressibility,degree of shrinkage and thermal expansion coefficient of the cutformation sheets 30 can be suppressed.

The thickness of the multilayer body 32 thus obtained by the laminationis preferred to be 1 mm or less on demand for making the size and heightof a multilayer ceramic substrate small. The lamination height of thecavity formation sheets (six cut formation sheets 10 and first compositegreen sheet 26) of the multilayer body 32 constituting the cavity is setin conformity to the size of an electronic device to be accommodated inthe cavity.

After the laminating step (S16), the pressing step (S17) is performed.The pressing step (S17) is a press-on step for the multilayer body 32produced in the laminating step (S16). The press-on step is performed,with the multilayer body placed in a die having upper and lower flatpunches. The preferable conditions of the press-on step include apressure of 30 to 80 MPa and a period of around 10 minutes. In thepresent embodiment, since the uppermost and lowermost layers of themultilayer body 32 are flat and further since the portion 31 a separatedby the cut 31 is left intact in the portion where the cavity is formed,pressure in the pressing step can be applied uniformly. Therefore, thereis no case where the opening of the cavity is deformed by collapse ordamaged by the pressure applied as in the prior art.

The firing step (S2) is then performed, in which the multilayer body 32pressed on in the pressing step (S17) is fired. The multilayer body 32is subjected to debinder treatment before the firing step. Theconditions of the debinder treatment may be generally adopted ones. Thefiring step is then performed to form a fired multilayer body 34. Theatmosphere in the firing step is not particularly restricted. When abase metal, such as nickel or nickel alloy, is used for the viaelectrode and internal electrode pattern, the atmosphere is preferred tobe a reduction atmosphere. The firing temperature is preferred to be inthe range of 800° C. to 1000° C. As a consequence, the conductivematerial and resistance material can be fired at the same time, and themultilayer ceramic substrate subsequently obtained can be used for LTCCmodules including high-frequency superposed modules, antenna switchmodules, filter modules, etc.

In the fired multilayer body 34 having undergone the firing step (S2),as shown in FIG. 6( b), the portion 30 a of the cut formation sheet 30inside the cut 31 projects from the cavity. The reason therefor is asfollows. When the multilayer body 32 is fired, the ceramic green sheetand the first composite green sheet 26 that are the dielectric layersheet and the cut formation sheet 30 are sintered and intended toshrink. At this time, the ceramic green sheet 21 is in intimate contactwith the lower shrinkage suppression green sheet 22. Since the shrinkagesuppression green sheet does not shrink at the firing temperature of thedielectric layer sheet, as described earlier, the shrinkage of theceramic green sheet 21 in the plane surface direction is suppressed.Since the portion 30 b of the cut formation sheet 30 outside the cut 31is in intimate contact with the uppermost composite green sheet 29, theshrinkage thereof is also suppressed. In addition, since the ceramicgreen sheet 21 is in intimate contact with the first fitting sheet 25 ofthe first composite green sheet 26, the shrinkage thereof is similarlysuppressed.

On the other hand, the portion 30 a of the cut formation sheet 30 insidethe cut 31 is not provided on the upper side thereof with a shrinkagesuppression sheet, the shrinkage thereof is not suppressed. Thus, theinside portion 30 a of the cut 31 is shrunk in the plane surfacedirection to separate from the outside portion 30 b of the cut 31. Thedegree of this shrinkage is larger toward the upper layer from the firstfitting sheet 25 on the bottom of the cavity, and the degree ofshrinkage in the thickness direction is made smaller by the amount ofthe inside portion 30 a of the cut 31 shrunk in the plane surfacedirection. Therefore, the first fitting sheet 25, second fitting sheet28 and the portion sandwiched between the two sheets (inside portion 30a of the cut 31) after being fired project from the surface of the firedmultilayer body 34.

As described above, the first fitting sheet 25, second fitting sheet 28and the portion sandwiched between the two sheets (inside portion 30 aof the cut 31) are brought to the state of shrinkage different from thatof the portion 30 b of the ceramic green sheet 21 and cut formationsheet 30 outside the cut 31. For example, the portion 30 a of the cutformation sheet 30 inside the cut 31 is completely separated from theoutside portion 30 b. Also at the cavity bottom, the first fitting 25 ismade fragile by the firing and the binding force at this portion becomesweak. Therefore, the first fitting sheet 25, second fitting sheet 28 andthe portion sandwiched between the two sheets (inside portion 30 a ofthe cut 31) filled in the cavity are enabled to fall off with a slightstimulus to form the cavity 11. Even in the case of the cavity having acomplicated shape, the inside portion 30 a of the cut 31 is enabled tofall off. In order to cause the inside portion 30 a of the cut 31 tofall off, a small force may be exerted onto it.

Specifically, as shown in FIG. 6( c), the first fitting sheet 25, secondfitting sheet 28 and the portion sandwiched between the two sheets(inside portion 30 a of the cut 31) are removed to form the cavity and,at the same time, the shrinkage compression sheet removal step (S4) isperformed when necessary. In the step (S4), the uppermost sheet 35 andthe lowermost sheet 36 of the fired multilayer body 34 (shrinkagecompression green sheet 22 and uppermost composite green sheet 29 thathave been fired) are removed through ordinary ultrasonic washing in asolvent or wet blasting. The wet blasting is a method comprisingaccelerating a liquid having an abrasive mixed in water with compressedair from a compressor and blowing the water against a substance to beprocessed to thereby perform both washing and surface treatmentsimultaneously. When the shrinkage suppression green sheet 22 is formedof a tridymite-silica-based material or cristobalite-silica-basedmaterial, since the major parts of the uppermost sheet 35 and lowermostsheet 36 after the firing exfoliate spontaneously, washing of theslightly remaining part will suffice.

Besides the steps described above, a cutting step, a polishing step,etc. are performed as occasion demands to obtain the multilayer ceramicsubstrate 1 shown in FIG. 1. The cutting step includes division with adiamond scriber and, when the fired multilayer body is thick, cutting bya dicing system. The polishing step is performed through the lappingprocess. The lapping process is a processing method for buffing theobject to be processed using a processed liquid containing abrasivecoating, with abrasive coating not contained in a rotary bed. Use of awet barrel is also available.

An electronic device 40 is mounted on the multilayer ceramic substrate 1produced. The state of the electronic device 40 mounted on the substrateis shown in FIG. 7. As shown in FIG. 7, the electronic device 40 isaccommodated in the cavity 11 of the multilayer ceramic substrate 1. Theelectronic device 40 is connected to electrodes (not shown) formed onthe multilayer ceramic substrate 1 with bonding wires 41. The electrodesinclude surface electrodes and via electrodes printed on the surface ofthe multilayer ceramic substrate 1 and internal electrodes printedinside the multilayer ceramic substrate 1. The multilayer ceramicsubstrate 1 thus fabricated by the method of the present embodimentpermits accommodation of an electronic device therein and satisfies thedemand of making the substrate small in size and height.

In the multilayer ceramic substrate fabricated by the production methoddescribed above, the cavity has a specific shape having superiority inthe property of sealing with a resin to the shape of the cavity of theprior art multilayer ceramic substrates. The shape of the cavity of themultilayer ceramic substrate fabricate will be described hereinafter.

The multilayer ceramic substrate 1 fabricated by the method according tothe first embodiment comprises plural (nine here) ceramic layers 2 to 10laminated and made integral. Of these ceramic layers 2 to 10, two lowerlayers 2 and 3 are formed with no through hole for formation of a cavityand are flat ceramic layers. Of the two, the upper ceramic layer 3 hasan upper surface 3 a, part of which is exposed to a cavity lower portionto constitute the cavity bottom. The remaining ceramic layers 4 to 10laminated on the ceramic layer 3 are formed respectively with throughholes corresponding to a cavity. These through holes are connectedcontiguously to form the cavity 11 as the prescribed space.

As already described in the production method, in fabricating themultilayer ceramic substrate 1, the firing step is conducted while thefirst fitting sheet 25, the uppermost layer of composite green sheet 29and shrinkage suppression green sheet 22 afford a binding force to thesubstrate green sheet to suppress the shrinkage in the in-planedirection. In this case, since the opposite ends of the multilayer bodyare bound by means of the shrinkage suppression green sheets during thestep of firing, the substrate green sheet after the step of firing isshrunk only in the width direction and would not be shrunk in thesurface direction.

When observing it in detail, however, while no virtually discernibleshrinkage of the substrate green sheet immediately close to theshrinkage suppression green sheets (first fitting sheet 25, uppermostlayer of composite green sheet 29 and shrinkage suppression green sheet22) in the surface direction is recognized, it can be recognized thatthe substrate green sheet shrinks only slightly in the surface directionwith an increasing distance from the shrinkage suppression green sheets.The surface direction shrinkage increases with increasing distance fromthe shrinkage suppression green sheets. For this, when observing theshape of the cavity 11 in detail, as typically shown in FIG. 8, thecavity has a larger opening diameter at the inside than at the openingimmediately close to the shrinkage suppression green sheets, like adrum-shaped cavity.

The description on this point will be given in more detail. In thecavity 11, the opening dimension W1 at an opening 11 a is smaller thanthe opening dimension W2 at a position 11 b midway in the depthdirection of the cavity 11. In other words, the opening area at theopening 11 a of the cavity 11 is smaller than the opening area at theposition 11 b midway in the depth direction of the cavity 11. In thisexample, the opening area of the cavity 11 is gradually increased up tothe position 11 b midway in the depth direction of the cavity and thengradually decreased up to the cavity bottom and, thus, the inner wall ofthe cavity 11 assumes a substantially circular arc in cross section.Thus, the portion of the cavity midway in the depth direction is bulgedout to shape a drum-shaped cavity.

The multilayer ceramic substrate 1 having the cavity 11 of the shapementioned above, owing to the specific shape, has a significant merit interms of reliability. As shown in FIG. 9, for example, when theelectronic device 40 is mounted within the cavity 11 and sealed with aresin 100, the opening dimension at the opening 11 a of the cavity issmaller than that of the cavity inside, the resin filled in the cavitywill not fall off at all. As described earlier, in the seal with theresin 100, the problem will arise in that the resin sealed exfoliatesand falls off, resulting from the difference in thermal expansioncoefficient between the ceramic sheets 2 to 10 constituting themultilayer ceramic substrate 1 and the resin 100 used for the seal. Thisproblem becomes conspicuous particularly when a temperature change isrepeated over a long period of time. In the multilayer ceramic substrate1, since the opening area at the opening 11 a of the cavity 11 issmaller than the opening area of the portion at the position 11 b midwayin the depth direction of the cavity 11, the resin filled and hardenedin the cavity cannot pass through because of the larger area of theinside of the cavity and is retained within the cavity.

The multilayer ceramic substrate 1 having the cavity 11 of the specificshape has not yet been materialized. This substrate 1 can be formedthrough the fact that the firing step is conducted, with the substrategreen sheet bound by means of the first fitting sheet 25, uppermostcomposite green sheet 29 and shrinkage suppression green sheet 22 andthe fact that the portion 31 separated by the cut 31 are left intact, inthe portion where the cavity is to be formed, in the form of an embeddedgreen sheet when forming a multilayer body before being fired so thatpressure may be exerted uniformly in the pressing step. Though thedetailed reasons for this is not explicitly ascertained, it hasexperimentally been confirmed that the shape of the cavity cannot beobtained only through the binding force by the shrinkage suppressiongreen sheets, but has been materialized for the first time through themethod of the present invention.

The second embodiment of the present invention will now be described.The difference thereof from the first embodiment is to form the cavityinto a multistage cavity (two-step cavity with two bottoms in thiscase). To be specific, the different points in step are to dispose afirst composite green sheet on the deepest bottom of the cavity, disposea second composite green sheet on the second bottom (step surface) andlaminate the cut formation sheets having through holes different in sizefrom each other.

In the present embodiment, a second composite green sheet 43 shown inFIG. 10( a) is formed in the composite green sheet formation step (S12).In producing the second composite green sheet 43, the ceramic greensheet 21 produced in the green sheet formation step (S11) is formed witha third through hole 44 that overlaps the first through hole 24 and islarger than the first through hole 24. The formation method of the thirdthrough hole 44 is the same as the formation method of the first throughhole 24.

The shrinkage suppression green sheet 22 produced in the green sheetformation step (S11) is cut into the same shape as the third throughhole 44 to form a third fitting sheet 45, which is fitted in the thirdthrough hole 44. In addition, the third fitting sheet 45 fitted isformed with a fourth through hole 46 formed at the same position as thefirst through hole 24 to have substantially the same shape as the firstthrough hole, in which fourth through hole the second fitting sheet 28obtained by cutting the ceramic green sheet 21 into substantially thesame shape as the fourth through hole is fitted. A second compositegreen sheet 43 is thus produced. In producing the second composite greensheet 43, a reverse procedure of first fitting the second fitting sheet28 in the fourth through hole 46 and then fitting the third fittingsheet 45 in the third through hole 44 may be adopted.

In the present embodiment, as shown in FIG. 10( b), a cut formationsheet (second cut formation sheet 47) different from the cut formationsheet 30 in the first embodiment is formed in the cut formation step(S13). The difference of the second cut formation sheet 47 and theprevious cut formation sheet 30 is the size of a cut 48 that is largerthan that of the cut 31. To be specific, the cut 48 in the second cutformation sheet 47 is formed at the same position as the third throughhole 44 of the second composite green sheet 43 to have substantially thesame shape as the third through hole 44.

An example of a multilayer body 49 having the sheets laminated in thepresent embodiment is shown in FIG. 11( a). The sheets are laminated inorder from below. That is to say, the shrinkage suppression green sheet22, ceramic green sheet 21, first composite green sheet 26, cutformation sheet 30, second composite green sheet 43, second cutformation sheet 47 and uppermost composite green sheet 29 are laminatedin the order mentioned from the lowermost layer. In this example, thenumber of each of the shrinkage suppression green sheet 22, firstcomposite green sheet 26, second composite green sheet 43 and uppermostcomposite green sheet 29 to be laminated is one. Of course, pluralnumber of each of these sheets may be laminated. The number of each ofthe ceramic green sheet 21, cut formation sheet 30 and second cutformation sheet 47 is determined depending on the interlayer electrodepattern configuration required for the multilayer ceramic substrate andthe size of an electronic device mounted on the inside of the substrateand is generally two or more. In this example, two ceramic green sheets21, six cut formation sheets 30 and four second cut formation sheets 47are laminated. Of course, the number of each of these sheets is notrestricted to this example, but is optional. The multilayer body 49 mayalso be formed with another cavity on the side of the shrinkagesuppression green sheet 22, for example, besides the cavity shown inFIG. 11( a).

When the multilayer body 49 has been fired, as shown in FIG. 11( b), theportion 49 a embedded in the cavity is shrunk in the surface directionto project from the cavity. The portion is removed in the same manner asin the first embodiment and, when necessary, the shrinkage suppressionsheet removal step (S4) is performed to complete a multilayer ceramicsubstrate 50 having a two-step cavity 51 with two bottoms as shown inFIG. 11( c).

An example in which an electronic device 40 is mounted on the multilayerceramic substrate 50 having the two-step cavity with two bottoms isshown in FIG. 12. As shown in FIG. 12, the electronic device 40 isaccommodated in a lower cavity portion 51 a. The electronic device 40 isconnected to the electrodes on the bottom of an upper cavity portion 51b with bonding wires 41. In this way, the multilayer ceramic substrate50 fabricated by the production method of the second embodiment enablesboth the electronic device 40 and the bonding wires 41 to beaccommodated in the inside thereof. Thus, the bonding wires and the likedo not protrude from the surface of the multilayer ceramic substrate.Also in a multilayer ceramic substrate provided therein with a pluralityof dielectric layers, an electronic device can be mounted at highdensity to satisfy the demand of making the size and height small.

By making use of the production method of a multilayer ceramic substrateaccording to the present embodiment, a multilayer ceramic substratehaving a three or more step cavity with three or more bottoms can befabricated. In the multilayer body formation step, for example, betweenthe uppermost composite green sheet and the ceramic green sheet providedat the same position as the second through hole with a cut ofsubstantially the same shape as the second through hole or with adiscontinuous portion, at least one third composite green sheet and atleast one overlapping ceramic green sheet are sandwiched. The thirdcomposite green sheet is obtained through the steps of providing aceramic green sheet with a fourth through hole overlapping the secondthrough hole and having a larger size than the second through hole,fitting a shrinkage suppression green sheet having substantially thesame shape and thickness in the fourth through hole, providing theshrinkage suppression green sheet fitted in the fourth through hole atthe same position as the second through hole with a fifth through holehaving substantially the same shape as the second through hole andfitting a ceramic green sheet having substantially the same shape andthickness as the fifth through hole in the fifth through hole. Theoverlapping ceramic green sheet is provided at the same position as thefourth through hole with a cut of substantially the same shape as thefourth through hole or with a discontinuous portion. In this state, thestep of pressing is performed in the lamination direction to obtain amultilayer body. The multilayer body is subjected to the cavityformation step to enable a three-step cavity with three bottoms to beformed.

Even in the case of forming a multistage cavity (two-step cavity withtwo bottoms in the present embodiment), the cavity has a specific shapeand therefore has superiority in resin-seal to the multistage cavity ofthe conventional multilayer ceramic substrate. The shapes of thecavities of the multilayer ceramic substrates fabricated will bedescribed below.

FIG. 13 is a diagram typically showing a multilayer ceramic substratehaving a multistage cavity. The multilayer ceramic substrate 50 isfabricated through the steps shown in FIG. 11 and has a two-step cavitywith two bottoms comprising cavity portions 51 a and 51 b similarly tothe multilayer ceramic substrate shown in FIG. 12. In each of the cavityportions 51 a and 51 b, the shrinkage in the surface direction graduallyincreases with an increasing distance from the shrinkage suppressinggreen sheet, and the opening size at each opening is smaller than thatat a position midway in the depth direction. To be specific, in thefirst step (upper) cavity portion 51 b, when the opening size at theopening is denoted by W3 and the opening size at a position midway inthe depth direction by W4, W3<W4. Similarly, in the second step (lower)cavity portion 51 a, when the opening size at the opening is denoted byW5 and the opening size at a position midway in the depth direction byW6, W5<W6. The cross-sectional shape of the sidewall of each of thecavity portions 51 a and 51 b is a circular arc and, therefore, theshape of each of the cavity portions assumes a pot or urceolate shape.

The second and subsequent step cavity portions (cavity portion 51 ahere) do not always assume a pot or urceolate shape, but may be of ashape having the largest opening area and gradually reducing the openingarea toward the depth direction as shown in FIG. 14. In this case, whenthe opening size at the opening is set to be W5 and the opening size ata position midway in the depth direction to be W6, W5>W6. The first step(upper) cavity portion 51 b assumes a pot or urceolate shape, whereasthe second step (lower) cavity portion 51 a assumes a shape of bowl. Bymaking the second and subsequent cavity portions bowl-shaped, wirebonding in mounting an electronic device on the cavity portion 51 a isready to perform, thereby enabling efficient device mounting.

In the multistage cavity 51 of the multilayer ceramic substrate 50,since at least the first step (upper) cavity portion 51 b has a shape ofa drum having the opening area larger at the inside than at the opening,reliable resin-seal in the cavity portions 51 a and 51 b can be secured.

In the production method of the first embodiment, for example, failureto achieve a balance of the upper and lower shrinkage suppression forcesdepending on the layer structure of the multilayer ceramic substratewill possibly deform the cavity bottom, as extremely depicted in FIG.15, for example. In such a case, the thickness of the shrinkagesuppressing green sheets sandwiching the cavity bottom is adjusted toavoid the deformation. The third embodiment of the present invention isdirected to this adjustment.

To be specific, as shown in FIG. 16, the thickness of the firstcomposite green sheet 26 having the shrinkage suppression green sheetpiece (first fitting sheet 25) fitted in the cavity formation portionthereof is adjusted. In this case, in order to compensate the change inthickness, though the thickness of the first fitting sheet 25 may onlybe adjusted, the thickness of the first composite green sheet as a wholemay be adjusted. Otherwise, as shown in FIG. 17, the thickness of theportion of the shrinkage suppression green sheet 22 corresponding to thecavity may be adjusted. In this case, the shrinkage suppression greensheet 22 shown in FIG. 17 comprises a lamination of a thin shrinkagesuppression green sheet 22 a and a green sheet 22 b having a throughhole at a cavity formation portion thereof and having a ceramic greensheet fitted in the through hole. With this, shrinkage suppression ofthe multilayer body as a whole and shrinkage suppression of the cavitybottom can independently be controlled.

In the shrinkage suppression green sheet 22 b, the shape of the ceramicgreen sheet to be fitted (shape of the through hole) may not be the sameas the cavity shape, but is determined in view of the balance of theshrinkage compression forces. The thickness of each of the first fittingsheet 25 and the shrinkage suppression green sheets 22 a and 22 b mayappropriately be set similarly in consideration of the balance of theshrinkage suppression forces.

The fourth embodiment of the present invention is directed to use of aburnable sheet. FIG. 18 shows the fundamental production process in thisembodiment that mainly comprises the steps of laminating and pressinggreen sheets and shrinkage suppressing green sheets that constituteceramic layers after being fired, firing the pressed body, removingembedded green sheets fired and removing the shrinkage suppression greensheets fired.

In fabricating a multilayer ceramic substrate, as shown in FIG. 18( a),a plurality of ceramic green sheets are laminated as green sheets for asubstrate in accordance with the number of the ceramic layersconstituting a multilayer ceramic substrate. Here, nine ceramic greensheets 61 to 69 are laminated. Each of the ceramic green sheets 61 to 69is formed through the steps of mixing ceramic powder, an organic binderand an organic solvent to form dielectric paste in the form of slurry,for example, and allowing the paste to grow on a PET sheet of support,for example, in accordance with the doctor blade method. Any of knownceramic powder and organic vehicles (organic binder and organic solvent)is usable in the present embodiment.

Of the ceramic green sheets 61 to 69, the two lower ceramic green sheets61 and 62 are not required to form a cavity formation through holetherein, but formed as ordinary flat green sheets. Of the two ceramicgreen sheets 61 and 62, the upper ceramic green sheet 62 constitutes thecavity bottom.

On the ceramic green sheet 62 constitutes the cavity bottom, laminatedare the seven remaining ceramic green sheets 63 to 69 given cuts 63 a to69 a (partially left out) of a prescribed shape corresponding to theshape of the cavity 11, respectively, to form separate portions 63 b to69 b (partially left out) that correspond to the cavity space. Thus, theseven ceramic green sheets 63 to 69 correspond to the cavity formationgreen sheets.

In the present embodiment, the portions 64 b to 69 b separated by thecuts 64 a to 69 a exclusive of the ceramic green sheet 63 in contactwith the ceramic green sheet 62 constituting the cavity bottom areutilized as embedded green sheets. However, this is not limitative. Aseparately formed embedded green sheet may be fitted in the throughholes corresponding to the cavity formed in the ceramic green sheets 64to 69. From the standpoint of productivity, however, utilization of theportions 64 b to 69 b separated by the cuts 64 a to 69 a as embeddedgreen sheets is advantageous.

The ceramic green sheet 63 in contact with the ceramic green sheet 62constituting the cavity bottom has its portion corresponding to thecavity removed therefrom to form a through hole, and a shrinkagesuppression green sheet piece 70 a and a burnable sheet piece 71 a eachhaving a shape corresponding to the through hole are fitted and buriedin the through hole. This is shown in detail in FIG. 19.

As shown in FIG. 19( a), a ceramic green sheet 63 is formed and, asshown in FIG. 19( b), the portion of the ceramic green sheetcorresponding to the cavity is punched out to form a through hole. Asshown in FIG. 19( c), a shrinkage suppression green sheet 70 is formedand, as shown in FIG. 19( d), a shrinkage suppression green sheet piece70 a punched out so as to have a shape substantially conforming to theshape of the through hole is formed. Similarly, as shown in FIG. 19( e),a burnable sheet 71 is formed and, as shown in FIG. 19( f), it ispunched out to form a burnable sheet piece 71 a having a shapesubstantially conforming to the through hole. Subsequently, as shown inFIG. 19( g), the shrinkage suppression green sheet piece 70 a andburnable sheet piece 71 a are fitted in the order mentioned and buriedin the through hole of the ceramic green sheet 63. Preferably, the totalthickness of the shrinkage suppression green sheet piece 70 a andburnable sheet piece 71 a conforms substantially to the thickness of theceramic green sheet 63.

The shrinkage suppression green sheet 70 (shrinkage suppression greensheet piece 70 a) is formed of a material not shrunk at the firingtemperature of the ceramic green sheets 61 to 69, such as tridymite orcristobalite, or of a composition containing quartz, molten quartz,alumina, mullite zirconia, aluminum nitride, boron nitride, magnesiumoxide, silicon carbide, etc. The shrinkage suppression green sheet piece71 a is disposed in contact with the ceramic green sheet (ceramic greensheet 62 in this case). The firing step is performed under theseconditions to suppress shrinkage of the ceramic green sheet 62 in thein-plane direction.

The burnable sheet 71 (burnable sheet piece 71 a) is formed of amaterial burnt down at the firing temperature of the ceramic greensheets 61 to 69, such as a resin material. Particularly preferably, theorganic binder contained in the ceramic green sheets 61 to 69 is used asthe material for the burnable sheet 71 (burnable sheet piece 71 a). Byso doing, the burnable sheet 71 (burnable sheet piece 71 a) is burntdown with exactitude in the firing step. While the burnable sheet piece71 a may be formed through punching the burnable sheet out as describedabove, it may be formed by the printing method, etc.

As described above, the ceramic green sheets 61 to 69 are laminated and,the shrinkage suppression green sheets 72 and 23 overlap the surfaces ofthe outermost green sheets 61 and 69, respectively. The shrinkagesuppression green sheet 72 and 73 are formed of the same material as theaforementioned shrinkage suppression green sheet 70. The shrinkagesuppression green sheet 73 disposed on the side of the ceramic greensheet 69 formed with a through hole (by the cut 69 a) corresponding tothe cavity is also formed with a through hole 73 corresponding to theopening of the cavity, in which an embedded ceramic green sheet piece 74separately punched out is fitted.

The multilayer body having these sheets laminated is in a state shown inFIG. 18( a), in which the shrinkage suppression green sheets 72 and 73are laminated, respectively, on the opposite surfaces of the multilayerbody having the plural ceramic green sheets 61 to 69 laminated, therebysuppressing shrinkage of the entire multilayer body in the in-planedirection. In addition, the shrinkage suppression green sheet piece 70 adisposed in the through hole of the ceramic green sheet 63 is in contactwith the ceramic green sheet 62 exposed to the cavity bottom, therebysuppressing shrinkage of this portion in the in-plane direction.

Though the space corresponding to the cavity is ordinarily formed as aspace (concave) at this stage, in the production method in thisembodiment, the portions 64 b to 69 b separated by the cuts 64 a to 69 aand the embedded ceramic green sheet piece 74 are disposed as theembedded green sheet. When seeing the entire shape of the multilayerbody, the multilayer body is formed as that flat without any concave.

The multilayer body having the ceramic green sheets 61 to 69 andshrinkage suppression green sheets 72 and 73 laminated is to be pressedin the pressing step preparatory to the firing step. At this time, whenthe multilayer body is formed with a concave corresponding to thecavity, the concave will possibly collapse to deform the opening of thecavity. In the present embodiment, however, since the multilayer bodyfabricated is uniform in thickness in the lamination direction andflattened over the entire thereof inclusive of the cavity portion owingto the presence of embedded green sheets, an ordinary flat mold die canbe used to press the multilayer body. Thus, the pressing step can beperformed with a simple means. While pressure is applied with themultilayer body sandwiched between the flat mold dies, as describedabove, the multilayer body coated with waterproof resin, etc. may besubjected to isostatic pressing.

After the firing step subsequent to the pressing step, as shown in FIG.18( b), the ceramic green sheets 61 to 69 are converted to ceramiclayers 2 to 10. At the time of firing, since the ceramic green sheets 61to 69 bound by the shrinkage suppression green sheets 72 and 73laminated thereon, they are shrunk only in the width direction and areseldom shrunk in the in-plane direction. The ceramic green sheet 62exposed to the cavity bottom is also suppressed from being shrunk in thein-plane direction.

In addition, the burnable sheet piece 71 intervening between theembedded green sheets (ceramic green sheets 64 to 69 and embeddedceramic green sheet piece 70 a) and the shrinkage suppression greensheet piece 70 a is burnt down before the ceramic green sheets 61 to 69are sintered. As a result, the binding force of the shrinkagesuppressing green sheet piece 70 a disposed on the cavity bottom is notexerted on the embedded green sheets to shrink the embedded green sheetsin the in-plane direction. A fired body 75 protrudes from the firedmultilayer body because the shrinkage in the thickness direction issmall. Since the binding force is not exerted, as described above, theembedded green sheets are shrunk and consequently no stress is appliedto the shrinkage suppression green sheet piece 70 a and also to theceramic green sheet 62 immediately under it. The flatness of the ceramiclayer 3 formed as a consequence of firing of the ceramic green sheet 62is not deteriorated.

Upon completion of the firing, the fired body 75 of the embedded greensheets is removed from the cavity space as shown in FIG. 18( c). Thefired body is separated from the shrinkage suppression green sheet piece70 a because the burnable sheet piece 71 a is burnt down and, therefore,can easily be removed by, for example, turning the fired multilayer bodyupside down.

Finally, residuals 76 of the fired shrinkage suppression green sheets 72and 73 and the fired shrinkage suppression green sheet piece 70 a areremoved to complete a multilayer substrate 1 having a cavity 11 as shownin FIG. 18( d). The residuals 76 can be removed with ease by some sortof cleaning step. The removal can be attained by stimulus of a degree byultrasonic cleaning, for example. Thus, as the cleaning step, the stepof ultrasonic cleaning in a solvent will suffice. When alumina-basedgreen sheets are used as the shrinkage suppressing green sheets,however, the residuals 76 do not exfoliate spontaneously. Therefore, theresiduals 76 are to be removed through polishing and cleaning by a wetblasting step.

The multilayer ceramic substrate 1 is excellent in dimensional accuracyand flatness of the cavity bottom has no deformation including collapseof the cavity opening and bulges around the cavity opening.

The fifth embodiment of the present invention is directed to use of aburnable sheet on each of the bottoms of the cavity portions inproducing a multilayer ceramic substrate having a multistage cavity (ofa two-step structure). In this case, as shown in FIG. 20( a), shrinkagesuppression green sheets 82 and 83 are laminated on the oppositesurfaces of a multilayer body 81 of ceramic green sheets and, at thesame time, shrinkage suppression green sheets 82 and 83 are laminated onboth surfaces of the multilayer body 81 of the ceramic green sheets,respectively, and shrinkage suppression green sheet pieces 84 and 85 andburnable sheet pieces 86 and 87 are disposed on the cavity bottom andthe stepped surface, respectively. The pressing step and firing step areperformed, with embedded green sheets 88 filled in the cavity space ofthe two-step structure. Also in the present embodiment, the flatness ofthe multilayer body is secured, and the pressing step is easy toperform.

Though a fired body 89 of the embedded green sheets after the firingstep protrudes form the multilayer body as shown in FIG. 20( b), it caneasily be removed by turning the multilayer body upside down in the samemanner as described above. A multilayer ceramic substrate 90 obtained isas shown in FGI. 20(c) and is excellent in entire dimensional accuracyas well as in dimensional accuracy of the bottom 91 a and steppedsurface 91 b of the cavity 91 and in their flatness. Incidentally, inthe case of the cavity 91 of the two-step structure, an electronicdevice is mounted on the bottom 91 a and the stepped surface 91 b isprovided with a conductive pattern connected to the electronic devicewith bonding wires.

The sixth embodiment of the present invention is directed to amultilayer ceramic substrate having a conductive pattern formed asstraddling the periphery of the cavity bottom.

FIG. 21( a) to FIG. 21( d) illustrate an example of the simplest modelof a multilayer ceramic substrate 101 having a cavity 111. In thisexample, plural (nine here) ceramic layers 102 to 110 are laminated andmade integral. Of these ceramic layers 102 to 110, two lower ceramiclayers 102 and 103 are flat ceramic layers provided with no through holefor the formation of a cavity. Of the two layers, the upper ceramiclayer 103 corresponds to a bottom formation ceramic layer, and part ofthe upper surface thereof faces the lower portion of the cavity andconstitutes the cavity bottom 111 a.

The remaining ceramic layers 104 to 110 laminated on the ceramic layer103 are provided with through holes 104 a to 110 a corresponding to thesidewall of the cavity 111 and constitute cavity formation ceramiclayers. Of these, the ceramic layer 104 corresponds to the first cavityceramic layer, and the ceramic layer 105 corresponds to the secondcavity ceramic layer. The surface of the ceramic layer 103 constitutingthe cavity bottom 111 a and the sidewalls of the through holes 104 a to110 a of the ceramic layers 104 to 110 made contiguous define the cavityspace. The shape of the opening of the cavity 111 is the same as that ofthe first embodiment, for example.

On the surface of the ceramic layer 113 is formed a conductive pattern112 that straddles the periphery of the bottom 111 a of the cavity 111.One end of the conductive pattern 112 is exposed to the bottom 111 a ofthe cavity 111 and connected to an electronic device accommodated in thecavity 111. The other end of the conductive pattern 112 is disposedbetween the ceramic layers 103 and 104 and connected to the internalelectrodes or wirings formed inside the multilayer ceramic substrate101. In FIG. 21, two sides of the square cavity 111 opposed when seenfrom top have two conductive patterns 112 in the form of a strip ofpaper, respectively, i.e. four in total. However, the shape and numberof the conductive patterns can arbitrarily be set. There is a case wherethe bottom 111 a of the cavity 111 is provided with via holes for heatradiation etc. though not shown.

In the multilayer ceramic substrate 101 of the present embodiment, atat-least two sides the conductive patterns overlap, the wall surface ofthe through hole 104 a of the ceramic layer 104 is disposed outside thewall surface of the through hole 105 a of the ceramic layer 105laminated immediately on the ceramic layer 104. Also in the presentembodiment, the opening area of the through hole 104 a of the ceramiclayer 104 is larger than that of the through hole 105 a of the ceramiclayer 105. Thus, the opening dimension of the cavity 111 is enlarged inthe vicinity of the cavity bottom 111 a.

The wall surface of the through hole 104 a formed in the ceramic layer104 may be positioned slightly outward of the wall surface of thethrough hole 105 a of the ceramic layer 105. A distance “A” between thewall surfaces 104 a and 105 a may be 0.1 mm or more, for example. Whenthe distance “A” is unduly large, since a dead space formed on thebottom of the cavity 111 becomes large, it is preferably 0.5 mm or less.

A multilayer ceramic substrate fabricated by each production methoddescribed later has a cavity of a specific shape. Specifically as istypically shown in FIG. 22, the opening area of the inside is largerthan that of the opening close immediately to the shrinkage compressiongreen sheet to form a drum-shaped cavity.

In the cavity 111, the opening dimension W1 at an opening 111 b issmaller than the opening dimension W2 at a position 111 c midway in thedepth direction of the cavity 111. In other words, the opening area atthe opening 111 b of the cavity 111 is smaller than the opening area atthe position 111 c midway in the depth direction of the cavity 111. Inthis example, the opening area of the cavity 111 is gradually increasedup to the position 111 c midway in the depth direction of the cavity andthen gradually decreased up to at least the ceramic layer 105 and, thus,the inner wall of the cavity 111 assumes a substantially circular arc incross section. Thus, the portion of the cavity midway in the depthdirection is bulged out to shape a drum-shaped cavity.

Incidentally, in the present embodiment, the position of the throughhole 104 a of the ceramic layer 104 laminated immediately on the cavitybottom formation ceramic layer 103 has nothing to do with the portion111 c midway in the depth direction of the cavity 111.

The multilayer ceramic substrate 101 having the cavity 111 of the shapedescribed above has a great merit in terms of reliability owing to itsshape specificity. As shown in FIG. 23, for example, when an electronicdevice 140 is mounted within the cavity 111 and sealed with a resin J,the opening dimension at the opening 111 b of the cavity 111 is smallerthan that of the cavity inside, the resin J filled in the cavity willnot fall off at all. As described earlier, in the seal with the resin Jrelative to the conventional shape, the problem will arise in that theresin sealed exfoliates and falls off, resulting from the difference inthermal expansion coefficient between the ceramic sheets 102 to 110constituting the multilayer ceramic substrate 101 and the resin J usedfor the seal. This problem becomes conspicuous particularly when atemperature change is repeated over a long period of time. In themultilayer ceramic substrate 101, since the opening area at the opening111 b of the cavity 111 is smaller than the opening area of the portionat the position 111 c midway in the depth direction of the cavity 111,the resin J filled and hardened in the cavity 111 cannot pass throughthe opening 111 b of the cavity 111 because of the larger area of theinside of the cavity and is retained within the cavity 111.

The multilayer ceramic substrate 101 having the configuration describedabove is formed through the production process performed. The productionprocess of the multilayer ceramic substrate in the present embodimentwill be described.

Also in the present embodiment, the non-shrinkage firing process isadopted, and the pressing and firing steps are performed, with theembedded green sheet disposed in a space corresponding to the cavity toeliminate collapse etc. at the pressing step in the same manner as inthe first embodiment. The step flowchart in the production process ispursuant to that shown in FIG. 2.

To be specific, in the green sheet formation step (S11) shown in FIG. 2,a ceramic green sheet (green sheet for a substrate) 121 shown in FIG.24( a) and a shrinkage suppression green sheet 122 shown in FIG. 24( b)are formed. Generally, these sheets 121 and 122 are formed as being inintimate contact with the surface of a support 123 that is a plasticsheet etc.

The ceramic green sheets 121 and shrinkage suppression green sheets 122are thus formed. The thickness of each sheet is preferred to be 20 μm to300 μm in consideration of the formation of a via electrode or aninternal electrode that will be described later.

After the fabrication of the ceramic green sheet 121 and shrinkagesuppression green sheet 122, a composite green sheet (green sheetcombining the ceramic green sheet with the shrinkage suppression greensheet) is fabricated utilizing the two sheets (S12). The composite greensheet fabricated here comprises a first composite green sheet (greensheet for formation of a first cavity) laminated immediately on thegreen sheet for formation of the cavity bottom and an uppermostcomposite green sheet laminated as an uppermost composite shrinkagesuppression green sheet.

A first composite green sheet 126 shown in FIG. 25( a) is produced.First, the ceramic green sheet 121 produced in the green sheet formationstep (S11) is formed with a first through hole 124. The first throughhole 24 may be formed by punching out a predetermined portion of theceramic green sheet 121, with the ceramic green sheet in intimatecontact with the surface of a support 123, with a die of a puncher orusing a laser beam or with a microdrill or by punching. The firstthrough hole 124 is formed to correspond to the shape of the cavitybottom, and the shape thereof is not particularly restricted, but may besquare, rectangular or circular.

The shrinkage suppression sheet 122 produced in the green sheetformation step (S11) is placed on the support 123 and cut into the sameshape as the first through hole 124 to obtain a first fitting sheet 125(corresponding to the shrinkage suppression green sheet piece). The cutfirst fitting sheet 125 is fitted in the first through hole 124 to forma first composite green sheet 126. At this time, in order to make thefirst composite green sheet 126 flat, preferably, the thickness of theceramic green sheet 121 is the same as that of the first fitting sheet125.

An uppermost composite green sheet 129 is produced in accordance withthe same production method as that of the first composite green sheet126. In the uppermost composite green sheet 129, as shown in FIG. 25(b), the shrinkage suppression green sheet 122 is formed with a throughhole in which a ceramic green sheet piece is fitted. To be specific, theshrinkage suppression green sheet 122 produced in the green sheetformation step (S11) is formed with a second through hole 127corresponding to the opening of the cavity. The production method of thesecond through hole 127 is the same as that of the first through hole124. The ceramic green sheet produced in the green sheet formation step(S11) is placed on the support and cut into the same shape as the secondthrough hole 127 to obtain a second fitting sheet 128. The cut secondfitting sheet 128 is fitted in the second through hole 127, and theresultant composite sheet is allowed to exfoliate from the support 123to form an uppermost composite green sheet 129. Also in this case, inorder to make the uppermost composite green sheet 129 flat, preferably,the thickness of the shrinkage suppression green sheet 122 is the sameas that of the second fitting sheet 128.

In the cut formation step (S13), the ceramic green sheet 121 is formedwith a cut to be used as a cavity formation green sheet. Specifically,in the cut formation step (S13), the ceramic green sheet 121 produced inthe green sheet formation step (S18) is formed with a cut (or adiscontinuous portion) 131 to form a cut formation sheet 130 as shown inFIG. 26. The cut 131 indicates the discontinuous portion pierced in thedirection of the thickness of the ceramic green sheet 121. Incidentally,the discontinuous portion includes what is not pierced in the sheetwidth direction. The end face of the portion 130 a defined by the cut131 is set to be at a position inside the wall surface of the firstthrough hole 124 of the first composite green sheet 126 at at-least theportion shown in FIG. 28 where the conductive pattern 112 formed on thecavity bottom formation green sheet 132 straddles the periphery 111 a ofthe cavity 111 when the cut formation sheet 130 has overlapped the caitybottom formation green sheet 132 shown in FIG. 27 that overlaps thefirst composite green sheet 126. The cut 131 is formed at the sameposition and in the same shape as the second through hole 127 to overlapthe second through hole 127 when the uppermost composite green sheet 129has overlapped the cut formation sheet 130.

The cut 131 may be formed by punching out a predetermined portion of theceramic green sheet 121, with the ceramic green sheet 121 in intimatecontact with the surface of the support 123, with a die of a puncher orusing a laser beam or with a microdrill or by punching.

In the cut formation step (S13), the cut may be inserted into theceramic green sheets 121 one by one or together in a lump. In eithercase, in the cut formation sheets 130, the inside portions 130 aseparated by the cuts 131 are left intact and utilized as embedded greensheets in the laminating and firing steps.

The first composite green sheet 126, cut formation sheets 130 andceramic green sheet constituting the bottom of the cavity (cavity bottomformation green sheet) that are ceramic green sheets constituting theceramic layers of a multilayer ceramic substrate after being fired(hereinafter referred to collectively as “dielectric layer sheets”) areprovided with a via hole, via electrode, internal electrode pattern,etc. Via electrode paste is filled and solidified by the stopgapprinting, for example, to form a via electrode. Internal electrode pasteis applied onto the ceramic green sheet, for example, in a prescribedpattern by the screen printing to form an internal electrode pattern.

Specifically, in the via hole formation step (S14), a via hole forforming a via electrode therein is formed in the dielectric layer sheet.In the conductor-printing step (S15), conductive paste is filled in thevia hole formed in the via hole formation step (S14) to form a viaelectrode. Also in the conductor-printing step (S15), an internalelectrode pattern is printed in a prescribed pattern on the surface ofthe dielectric layer sheet. Particularly in the conductor-printing step(S15), as shown in FIG. 27, conductive patterns 112 are formed on theceramic green sheet 132 to fabricate a cavity bottom formation greensheet 132. The conductive patterns 112 are formed as straddling theperiphery (shown by dashed line in FIG. 27) of the region constitutingthe bottom 111 a of the cavity 111 in the fired multilayer ceramicsubstrate.

After the formation of the via electrode and internal electrode patternon each of the dielectric layer sheets, the sheets are laminated in thelaminating step (S16) to form a multilayer body 133. The configurationsof the multilayer body from the laminating step (16) to the shrinkagesuppression sheet removal step (S4) are shown in FIG. 28( a) to FIG. 28(d). Incidentally, the step shown in FIG. 28( c) and the step shown inFIG. 28( d) may be performed inversely in order or simultaneously.

In the laminating step (S16), as shown in FIG. 28( a), a shrinkagesuppression green sheet 122, ceramic green sheet 121, cavity bottomformation green sheet 132, first composite green sheet 126, cutformation sheet 130 and uppermost composite green sheet 129 arelaminated in the order mentioned from the lowermost layer.

In the present embodiment, at the portion where the periphery of thebottom 111 a of the cavity 111 and the conductive pattern 112 overlap ina planar state in the multilayer ceramic substrate having undergone thefiring step, it is required to set the end face of the first fittingsheet 125 (shrinkage suppression sheet piece) to be positioned outsidethe end face of the inside portion 130 a (embedded green sheet) of thecut 131 formed in the cut formation sheet 130 laminated immediately onthe first fitting sheet 125. In the present embodiment, as shown in FIG.28( a), it is set that the size of the first fitting sheet 125(shrinkage suppression sheet piece) is larger than that of the portion(embedded green sheet) separated by the cut 131 from the cut formationsheet 130 laminated-thereon.

The end face of the first fitting sheet 125 (shrinkage compression sheetpiece) may be positioned slightly outside the end face of the insideportion 130 a of the cut 131 (embedded green sheet) laminatedimmediately thereon. The sizes of the first fitting sheet 125 and insideportion 130 a of the cut 131 of the cut formation sheet 130 may be setso that the distance “A” between the wall surface of the through hole104 a of the ceramic layer 104 and the wall surface of the through hole105 of the ceramic layer 105 may be 0.1 mm to 0.5 mm.

The number of each sheet may be singular or plural. In the exampleshown, laminated on a ceramic green sheet 121 is a cavity bottomformation green sheet 132 on which a first composite green sheet 126 andsix cut formation sheets 130 are laminated. Therefore, the nine sheetscorrespond to green sheets for a substrate, and the first compositegreen sheet 126 and the six cut formation sheets 130 correspond to greensheets for formation of a cavity. Of the cavity formation green sheets,the first composite green sheet 126 corresponds to a first cavityformation green sheet, and the cut formation sheets 130 correspond tothe second cavity formation sheets. The configuration of the multilayerbody 133 may be an upside-down configuration or a configuration havingthe same configuration added across the shrinkage suppression greensheet 122.

When laminating two or more cut formation sheets 130, for example, thesemay be formed of the same material or differ materials. In the lattercase, however, they are preferred to be substantially the same incompressibility at the time of pressing and in degree of shrinkage andthermal expansion coefficient at the time of firing. By so doing, warpof the substrate resulting from the difference in compressibility,degree of shrinkage and thermal expansion coefficient of the cutformation sheets 130 can be suppressed.

The entire thickness of the multilayer body 133 thus obtained by thelamination is preferred to be 1 mm or less on demand for making the sizeand height of a multilayer ceramic substrate small. The laminationheight of the cavity formation sheets (six cut formation sheets 130 andfirst composite green sheet 126) of the multilayer body 133(corresponding to the cavity depth) is set in conformity to the size ofan electronic device to be accommodated in the cavity.

After the laminating step (S16), the pressing step (S17) is performed.The pressing step (S17) is a press-on step for the multilayer body 133produced in the laminating step (S16). The press-on step is performed,with the multilayer body placed in a die having upper and lower flatpunches. The preferable conditions of the press-on step include apressure of 30 to 80 MPa and a period of around 10 minutes. In thepresent embodiment, since the uppermost and lowermost layers of themultilayer body 133 are flat and further since the portion 131 aseparated by the cut 131 is left intact in the portion where the cavityis formed as the embedded green sheet filled in the cavity, pressure inthe pressing step can be applied uniformly. Therefore, there is no casewhere the opening of the cavity is deformed by collapse or damaged bythe pressure applied as in the prior art.

The firing step (S2) is then performed, in which the multilayer body 133pressed on in the pressing step (S17) is fired. Generally, themultilayer body 133 is subjected to debinder treatment before the firingstep. The conditions of the debinder treatment may be generally adoptedones. The firing step is then performed to form a fired multilayer body134. The atmosphere in the firing step is not particularly restricted.When a base metal, such as nickel or nickel alloy, is used for the viaelectrode and internal electrode pattern, the atmosphere is preferred tobe a reduction atmosphere. The firing temperature is preferred to be inthe range of 800° C. to 1000° C. As a consequence, the conductivematerial and resistance material can be fired at the same time, and themultilayer ceramic substrate subsequently obtained can be used for LTCCmodules including high-frequency superposed modules, antenna switchmodules, filter modules, etc.

In the fired multilayer body 134 having undergone the firing step (S2),as shown in FIG. 28( b), the portion 130 a of the cut formation sheet 30inside the cut 31 projects from the cavity. The reason therefor is asfollows. When the multilayer body 133 is fired, the ceramic green sheet121, cavity bottom formation green sheet 132, first composite greensheet 126 and cut formation green sheet 130 that are the dielectriclayer sheets are sintered and intended to shrink. At this time, theceramic green sheet 121 is in intimate contact with the lower shrinkagesuppression green sheet 122. Since the shrinkage suppression green sheet122 does not shrink at the firing temperature of the dielectric layersheets, as described earlier, the shrinkage of the ceramic green sheet121 in the plane surface direction is suppressed. Since the portion 130b of the cut formation sheet 130 outside the cut 131 is in intimatecontact with the uppermost composite green sheet 129, the shrinkagethereof is also suppressed. In addition, at the bottom of the cavity,since the cavity bottom formation 132 is in intimate contact with thefirst fitting sheet 125 of the first composite green sheet 126, theshrinkage thereof is similarly suppressed.

On the other hand, the portion 130 a of the cut formation sheet 130inside the cut 131 is provided on the upper side thereof with noshrinkage suppression sheet, the shrinkage thereof is not suppressed.Thus, the inside portion 130 a of the cut 131 is shrunk in the planesurface direction to separate from the outside portion 130 b of the cut131. The degree of this shrinkage is larger toward the upper layer fromthe first fitting sheet 125 on the bottom of the cavity, and the degreeof shrinkage in the thickness direction is made smaller by the amount ofthe inside portion 130 a of the cut 131 shrunk in the plane surfacedirection. Therefore the first fitting sheet 125, second fitting sheet128 and the portion sandwiched between the two sheets (inside portion130 a of the cut 131) after being fired project from the surface of thefired multilayer body 134.

As shown in FIG. 29, for example, when the first fitting sheet(shrinkage suppression sheet piece) 303 and the region of the cutformation sheet surrounded by the cut (embedded green sheet) 309 areformed in substantially the same shape and when the end face of theshrinkage suppression sheet piece 303 is flush with the end face of theembedded green sheet 309 thereon, a problem of disconnection of theconductive pattern 301 disposed as straddling the periphery of thecavity bottom will be imposed. Of the cavity bottom formation greensheets 302, the region (cavity bottom) on which the first fitting sheet303 is disposed is seldom shrunk in the in-plane direction owing to astrong binding force of the first fitting sheet 303, whereas since thebinding force of the shrinkage suppression green sheet 306 and uppermostcomposite green sheet 307 relative to the region around the side wall ofthe cavity (cut formation sheets 304, first composite green sheet 305and bottom formation green sheets 302) tends to be weakened toward thecenter of the lamination direction, the lower end 308 of the sidewall ofthe cavity small in binding force is greatly shrunk in the in-planedirection apart from the cavity. As a consequence, stress isconcentrated in the periphery of the cavity bottom to inducedisconnection of the conductive pattern 301 disposed at such periphery.

In the present embodiment, therefore, the end face of the first fittingsheet (shrinkage suppression sheet piece) 125 is disposed outside theend face of the inside portion (embedded green sheet) 130 a of the cut131 of the cut formation sheet 130 in at least the portion where theperipheral portion of the cavity bottom and the conductive patternoverlap. With this, part of the upper surface of the first fitting sheet125 is in surface contact with the lower surface of the lowermost layerof the cut formation sheets 130, and the contact surface 125 a causesthe binding force of the first fitting sheet 125 to extend to the regionof the plurality of cut formation sheets 130 laminated thereon in thevicinity of the cavity sidewall. For this reason, the first fittingsheet 125 can bind the shrinkage of the cut formation sheets (lower endof the cavity sidewall) in the in-plane direction to weaken the stressapplied to the conductive pattern 112, thereby suppressing disconnectionof the conductive pattern 112.

As described above, the first fitting sheet 125, second fitting sheet128 and the portion sandwiched between the two sheets (inside portion130 a of the cut 131) are brought to the state of shrinkage differentfrom that of the portion 130 b of the ceramic green sheet 121 and cutformation sheet 130 outside the cut 131. For example, the portion 130 aof the cut formation sheet 130 inside the cut 131 is completelyseparated from the outside portion 130 b. Also at the cavity bottom, thefirst fitting 125 is made fragile by the firing and the binding force atthis portion becomes weak. As is shown in FIG. 28( c), therefore, thefirst fitting sheet 125, second fitting sheet 128 and the portionsandwiched between the two sheets (inside portion 130 a of the cut 131)filled in the cavity are enabled to fall off with a slight stimulus.Even in the case of the cavity having a complicated shape, the insideportion 130 a of the cut 131 is enabled to fall off. In order to causethe inside portion 130 a of the cut 131 to fall off, a small force maybe exerted onto it.

Specifically, as shown in FIG. 28( c), the first fitting sheet 125,second fitting sheet 128 and the portion sandwiched between the twosheets (inside portion 130 a of the cut 131) are removed to form thecavity and, at the same time, the shrinkage compression sheet removalstep (S4) is performed when necessary. In the step (S4), as is shown inFIG. 28( d), the uppermost sheet 135 and the lowermost sheet 136 of thefired multilayer body 134 (shrinkage compression green sheet 122 anduppermost composite green sheet 129 that have been fired) are removedthrough ordinary ultrasonic washing in a solvent or wet blasting. Thewet blasting is a method comprising accelerating a liquid having anabrasive mixed in water with compressed air from a compressor andblowing the water against a substance to be processed to thereby performboth washing and surface treatment simultaneously. When the shrinkagesuppression green sheet is formed of a tridymite-silica-based orcristobalite-silica-based material, since the major parts of theuppermost sheet 135 and lowermost sheet 136 after the firing stepexfoliate spontaneously, washing of the slightly remaining part willsuffice.

As shown in FIG. 28( c), of the fired body of the first fitting sheet125, at least part overlapping the outside portion 130 b of the cutforming sheets 130 is collapsed, and the collapsed part though not shownremains as the residual in a position before falling-off of the insideportion 130 a (dead space in the vicinity of the bottom of the cavity111). Preferably, the residual is removed by cleaning with wet blasting.The removal of the residual of the first fitting sheet 125 and thecleaning removal of the uppermost sheet 135 and lower most sheet 136 ofthe fired multilayer body 134 (fired bodies of the uppermost green sheet129 and shrinkage suppression green sheet 122) may be performed eithersimultaneously or separately.

Besides the steps described above, a cutting step, a polishing step,etc. are performed as occasion demands to obtain the multilayer ceramicsubstrate 1 shown in FIG. 21. The cutting step includes division with adiamond scriber and, when the fired multilayer body 134 is thick,cutting by a dicing system. The polishing step is performed through thelapping process, for example. The lapping process is a processing methodfor buffing the object to be processed using a processed liquidcontaining abrasive coating, with abrasive coating not contained in arotary bed. Use of a wet barrel is also available.

An electronic device 140 is mounted on the multilayer ceramic substrate101 produced. The state of the electronic device 40 mounted on thesubstrate is shown in FIG. 30. As shown in FIG. 30, the electronicdevice 140 is accommodated in the cavity 111 of the multilayer ceramicsubstrate 101. The bottom surface of the electronic device 140 isconnected to the conductive pattern 112 exposed to the bottom 111 a ofthe cavity 111 and the electronic device 140 is also connected toelectrodes (not shown) formed on the multilayer ceramic substrate 101with bonding wires 141. The electrodes include surface electrodes andvia electrodes printed on the surface of the multilayer ceramicsubstrate 101 and internal electrodes printed inside the multilayerceramic substrate 101. The multilayer ceramic substrate thus fabricatedby the method of the present embodiment permits accommodation of anelectronic device therein and satisfies the demand of making thesubstrate small in size and height.

The seventh embodiment of the present invention is directed to anexample in which the wall surface of the through hole in the ceramiclayer for forming a first cavity is disposed outside the wall surface ofthe through hole in the ceramic layer for forming a second cavity overthe entire periphery of the cavity bottom. The description of part ofthe present embodiment overlapping the sixth embodiment will be omitted.

In the sixth embodiment, since there is no concern that disconnectionarises at the sides on which no conductive pattern exists, the firstfitting sheet 125 corresponding to the shrinkage suppression green sheetpiece and embedded green sheet 130 a are used to allow their end facesto be in flush with each other. For this reason, the cut formation sheet130 corresponding to this portion is not bound by the first fittingsheet 125 to be greatly shrunk in the in-plane direction. When aninternal electrode pattern is interposed between the lower ceramiclayers of the sidewalls of the cavity, for example, there is apossibility of the internal electrode pattern being disconnected.

In the present embodiment, therefore, the end face of the first fittingsheet 125 is positioned outside the end face of the embedded green sheet130 a over the entire periphery of the bottom 111 a of the cavity 111 todispose the wall surface of the through hole 104 a of the ceramic layer104 outside the wall surface of the through hole 105 a of the ceramiclayer 105. Specifically, as shown in FIG. 31, in the multilayer ceramicsubstrate 145 of the present embodiment, the wall surface of the throughhole 104 a of the ceramic layer is positioned outside the wall surfaceof the through hole 105 a of the ceramic layer 105 even at the peripheryof the bottom 111 a of the cavity 111 where no conductive pattern 112 isformed.

To obtain the multilayer ceramic substrate 145 as shown in FIG. 31, itmay be set that the entire end face of the first fitting sheet 125 ispositioned outside the inside portion (embedded green sheet) 130 a ofthe cut 131 of the cut formation sheet 130 when the first fitting sheet126 and cut formation sheet 131 have been laminated with each other.With this, since the first fitting sheet 125 binds the entirety in thevicinity of the inner periphery of the cut formation sheet 130,shrinkage of the cut formation sheet 130 in the in-plane direction inthe entire periphery of the bottom 111 a of the cavity 111 is suppressedto enable not only the conductive pattern 112 but also the internalelectrode pattern provided in the lower portion of the sidewall of thecavity to be suppressed from disconnection.

FIG. 32 shows an example in which all sides of the periphery of a cavity111 having a square opening are provided with conductive patterns 112.In a multilayer ceramic substrate 101 shown in FIG. 32, the wall surfaceof the through hole 104 a of the ceramic layer 104 is positioned outsidethe wall surface of the through hole 105 a of the ceramic layer 105 overthe entire periphery of the bottom 111 a of the cavity 111 to reliablysuppress disconnection of the conductive patterns 112 exposed to thecavity bottom or the internal electrode pattern.

As shown in FIG. 33, for example, a conductive pattern 112 may be formedentirely on the bottom 111 a of the cavity 111. Also in this case, sincein a multilayer ceramic substrate 101 obtained the wall surface of thethrough hole 104 a of the ceramic layer 104 in at least the portionoverlapping the conductive pattern 112 is disposed outside the wallsurface of the through hole 105 a of the ceramic layer 105,disconnection of the conductive patterns or internal electrode patterncan reliably be suppressed.

The eighth embodiment of the present invention will be described. Thedifference between the sixth embodiment and the present embodiment isthat the present embodiment adopts a multistage cavity (two-step cavitywith two bottoms).

A multilayer ceramic substrate having a cavity with two bottoms will bedescribed hereinafter with reference to FIG. 34. The multilayer ceramicsubstrate 150 shown in FIG. 34 has a cavity 151 with two bottoms andcomprises plural (14 here) ceramic layers laminated and made integral. Aceramic layer 103 corresponds to the cavity bottom formation ceramiclayer and a part thereof is exposed to the cavity bottom to constitutethe deepest bottom 151 a of the cavity 151 with two bottoms. Of theceramic layers constituting the multilayer ceramic substrate 150, theconfiguration of the ceramic layers 102 to 109 is substantially the sameas that of the sixth embodiment. Part of the ceramic layer 110constitutes a bottom 151 a of the first-step bottom 151 a of the cavity151 with two bottoms. Therefore, the ceramic layer 110 corresponds to acavity bottom formation ceramic layer. The surface of the ceramic layer110 is provided thereon with a conductive pattern 152.

The ceramic layers 153 to 157 laminated on the ceramic layer 110 areprovided with through holes 153 a to 157 a and correspond to cavityformation ceramic layers. The sidewalls of the through holes 153 a to157 a of the ceramic layers 153 to 157 made contiguous define theshallower space of the two-step cavity 151.

In the multilayer ceramic substrate 150 of the present embodiment, atthe portion where the conductive pattern 152 straddles the periphery ofthe first step bottom 51 b, the wall surface of the through hole 153 aof the ceramic layer 153 in contact with the ceramic layer 110 ispositioned outside the wall surface of the through hole 154 a of theceramic layer 154.

In fabricating the multilayer ceramic substrate of the presentembodiment, a first composite green sheet is disposed on the deepestbottom of the cavity, a second composite green sheet is disposed on thefirst bottom (step surface) and the cut formation sheets having throughholes different in size from each other to conform to the dimensions ofthe multistage cavity portions are laminated thereon.

FIG. 35 shows the detailed shape of the cavity of the multilayer ceramicsubstrate shown in FIG. 34. Here, in each of the cavity portions 151 cand 151 d, the shrinkage in the surface direction gradually increaseswith an increasing distance from the shrinkage suppressing green sheet,and the opening size at each opening is smaller than that at a positionmidway in the depth direction. In this embodiment, the first step cavityportion 151 c has a shape bulged at a position midway in the depthdirection, and the opening area of the cavity portion 151 c increasesgradually up to the midway position and then decreases gradually up tothe penultimate cavity formation layer of the layers defining the firststep cavity 151 c. To be specific, in the first step cavity portion 151b, when the opening size at the opening is denoted by W3 and the openingsize at a position midway in the depth direction by W4, W3<W4.Similarly, in the second step cavity portion 151 d, when the openingsize at the opening is denoted by W5 and the opening size at a positionmidway in the depth direction by W6, W5<W6. The cross-sectional shape ofthe sidewall of each of the cavity portions 151 c and 151 d is acircular arc and, therefore, the shape of each of the cavity portions151 c and 151 d assumes a pot or urceolate shape.

The second and subsequent step cavity portions (cavity portion 151 dhere) do not always assume a pot or urceolate shape, but may be of ashape having the largest opening area and gradually reducing the openingarea toward the depth direction as shown in FIG. 36. In this case, whenthe opening size at the opening is set to be W5 and the opening size ata position midway in the depth direction to be W6, W5>W6. The first stepcavity portion 151 c assumes a pot or urceolate shape, whereas thesecond step cavity portion 151 d assumes a shape of bowl. By making thesecond and subsequent cavity portions bowl-shaped, wire bonding inmounting an electronic device on the cavity portion 151 d is ready toperform, thereby enabling efficient device mounting.

In the multistage cavity 151 of the multilayer ceramic substrate 150,since at least the first step cavity portion 151 c has a shape of a drumhaving the opening area larger at the inside than at the opening,reliable resin-seal in the cavity portions 151 c and 151 d can besecured.

A production method of the multilayer ceramic substrate 150 having theconfiguration described above will be described. The difference thereoffrom the sixth embodiment is to form the cavity into a multistage cavity(two-step cavity with two bottoms in this case). To be specific, thedifferent points in step are to dispose a first composite green sheet onthe deepest bottom of the cavity, dispose a second composite green sheeton the first step bottom (step surface) and laminate the cut formationsheets having through holes different in size from each other.

In the present embodiment, a second composite green sheet 143 shown inFIG. 37( a) is formed in the composite green sheet formation step (S12).In producing the second composite green sheet 143, the ceramic greensheet 121 produced in the green sheet formation step (S11) is formedwith a third through hole 144 that overlaps the first through hole 124and is larger than the first through hole 124. The formation method ofthe third through hole 144 is the same as the formation method of thefirst through hole 124.

The shrinkage suppression green sheet 122 produced in the green sheetformation step (S11) is cut into the same shape as the third throughhole 144 to form a third fitting sheet 145, which is fitted in the thirdthrough hole 144. In addition, the third fitting sheet 145 fitted isformed with a fourth through hole 146 formed at the same position as thecut 131 to have substantially the same shape as the cut, in which fourththrough hole the second fitting sheet 128 obtained by cutting theceramic green sheet 121 into substantially the same shape as the fourththrough hole 146 is fitted. A second composite green sheet 143 is thusproduced. In producing the second composite green sheet 143, a reverseprocedure of first fitting the second fitting sheet 128 in the fourththrough hole 146 and then fitting the third fitting sheet 145 in thethird through hole 144 may be adopted.

In the present embodiment, as shown in FIG. 37( b), a cut formationsheet (second cut formation sheet 147) different from the cut formationsheet 130 in the sixth embodiment is formed in the cut formation step(S13). The difference between the second cut formation sheet 147 and theprevious cut formation sheet 130 is the size of a cut 148 that is largerthan that of the cut 131. To be specific, the cut 148 in the second cutformation sheet 147 overlaps the third through hole 144 of the secondcomposite green sheet 143 and has a size smaller than that of the thirdthrough hole 144. Also in the second cut formation sheet 147 similarlyto the cut formation sheet 130, a portion 147 a separated by a cut 148is left intact and utilized as embedded green sheets in the laminatingand firing steps.

In the conductor-printing step (S15), as shown in FIG. 38, conductivepatterns 152 are formed on the surface of the uppermost cut formationsheet 130 as straddling the periphery of the cavity bottom 151 b tofabricate a second cavity bottom formation green sheet 158. Theconductive patterns 112 are formed on the surface of the green sheet 121in the same manner as in the sixth embodiment to form a bottom formationgreen sheet 132.

In the present embodiment, it is necessary to pay attention to the sizeof the third fitting sheet 145 (third through hole 144) to be fitted inthe second composite sheet 143 in the green sheet formation step (S11)and to the region of the cut 148 formed in the second cut formationsheet 147 in the cut formation step (S13). Specifically, when the secondcomposite sheet 143 and second cut formation sheet 147 have beenlaminated on the second bottom formation green sheet 158, at at-leastthe portion where the conductive pattern 152 is disposed as straddlingthe periphery of the first step bottom 151 b, it is set that the endface of the third fitting sheet 145 (third through hole 144) in thesecond composite sheet 143 is positioned outside the end face of theportion 147 a of the second cut formation sheet 147 separated by the cut148. Incidentally, when there are an inner end face and an outer endface like the third fitting sheet 145, the outer end face opposed to thesidewall of the cavity may be disposed outside the end face of theportion 147 a separated by the cut 148.

An example of the multilayer body 154 having the sheets laminated in thepresent embodiment is shown in FIG. 39( a). The sheets constituting themultilayer body 154 are laminated in order from below. That is to say,the shrinkage suppression green sheet 122, ceramic green sheet 121,cavity bottom formation green sheet 132, first composite green sheet126, cut formation sheet 130, second cavity bottom formation green sheet158, second composite green sheet 143, second cut formation sheet 147and uppermost composite green sheet 129 are laminated in the ordermentioned from the lowermost layer. Incidentally, the number of each ofthe shrinkage suppression green sheet 122, cavity bottom formation greensheet 132, first composite green sheet 126, second cavity bottomformation green sheet 158, second composite green sheet 143 anduppermost composite green sheet 129 to be laminated is one. Of course,plural number of each of these sheets may be laminated. The number ofeach of the ceramic green sheet 121, cut formation sheet 130 and secondcut formation sheet 147 is determined depending on the interlayerelectrode pattern configuration required for the multilayer ceramicsubstrate and the size of an electronic device mounted on the inside ofthe substrate and is generally two or more. In this example, one ceramicgreen sheet 121, five cut formation sheets 130 and four second cutformation sheets 147 are laminated. Of course, the number of each ofthese sheets is not restricted to this example, but is optional. Themultilayer body 154 may also be formed with another cavity on the sideof the shrinkage suppression green sheet 122, for example, besides thecavity shown in FIG. 39( a).

When the multilayer body 154 has been fired, a fired multilayer body 155shown in FIG. 39( b) is obtained. In the fired multilayer body 155, theportion 156 a filled in the cavity is shrunk in the surface direction toproject from the cavity. The portion is removed in the same manner as inthe sixth embodiment and, when necessary, the shrinkage suppressionsheet removal step (S4) is performed to complete a multilayer ceramicsubstrate 150 having a two-step cavity 151 with two bottoms as shown inFIG. 34.

An example in which an electronic device 140 is mounted on themultilayer ceramic substrate 150 having the two-step cavity 151 with twobottoms is shown in FIG. 40. As shown in FIG. 40, the electronic device140 is accommodated in a lower cavity portion. The electronic device 140is connected to the conductive pattern 152 exposed to the bottom 151 aof an upper cavity portion with bonding wires 141. In this way, themultilayer ceramic substrate 150 fabricated by the production method ofthe present embodiment enables both the electronic device 140 and thebonding wires 141 to be accommodated in the inside thereof. Thus, thebonding wires and the like do not protrude from the surface of themultilayer ceramic substrate. Also in a multilayer ceramic substrateprovided therein with a plurality of dielectric layers, an electronicdevice can be mounted at high density to satisfy the demand of makingthe size and height small.

Since the end face of the third fitting sheet 145 is disposed outsidethe end face of the portion 147 a of the second cut formation sheet 147separated by the cut 148, the binding force of the third fitting sheet145 extends to the plurality of second cut formation sheets 147laminated thereon. For this reason, the shrinkage of the second cutformation sheets 147 in the direction apart from the cavity issuppressed to weaken the stress applied to the conductive pattern 152 onthe surface of the first step bottom 151 b, thereby suppressingdisconnection of the conductive pattern 152.

By making use of the production method of a multilayer ceramic substrateaccording to the present embodiment, a multilayer ceramic substratehaving a three or more step cavity with three or more bottoms can befabricated. In the multilayer body formation step, for example, betweenthe uppermost composite green sheet and the ceramic green sheet providedat the same position as the third through hole with a cut ofsubstantially the same shape as the third through hole or with adiscontinuous portion, at least one third composite green sheet and atleast one overlapping ceramic green sheet are sandwiched. The thirdcomposite green sheet is obtained through the steps of providing aceramic green sheet with a fifth through hole overlapping the thirdthrough hole and having a larger size than the third through hole,fitting a shrinkage suppression green sheet having substantially thesame shape and thickness in the fifth through hole, providing theshrinkage suppression green sheet fitted in the fifth through hole atthe same position as the cut 148 with a sixth through hole havingsubstantially the same shape as the cut and fitting a ceramic greensheet having substantially the same shape and thickness as the sixththrough hole in the sixth through hole. The overlapping ceramic greensheet is provided at the same position as the fifth through hole with acut of substantially the same shape as the fourth through hole or with adiscontinuous portion. In this state, the step of pressing is performedin the lamination direction to obtain a multilayer body. The multilayerbody is subjected to the cavity formation step to enable a three-stepcavity with three bottoms to be formed.

When a conductive pattern is formed on the uppermost bottom asstraddling the boundary portion between the uppermost bottom and thesidewall, similarly to the production method of a multilayer ceramicsubstrate having a two-step cavity, the end face of a fitting sheet(shrinkage suppression green sheet piece) fitted in a third compositegreen sheet is disposed outside the end face of a cut or discontinuousportion (embedded green sheet) of the ceramic green sheet laminatedthereon. With this, disconnection of the conductive pattern formed onthe uppermost step bottom can be suppressed.

In the production method of the sixth embodiment, for example, failureto achieve a balance of the upper and lower shrinkage suppression forcesdepending on the layer structure of the multilayer ceramic substratewill possibly deform the cavity bottom, as extremely depicted in FIG.41, for example. In such a case, the thickness of the shrinkagesuppressing green sheets sandwiching the cavity bottom is adjusted toavoid the deformation. The ninth embodiment of the present invention isdirected to this adjustment.

To be specific, as shown in FIG. 42, the thickness of the firstcomposite green sheet 126 having a shrinkage suppression green sheetpiece (first fitting sheet 125) fitted in the cavity formation portionthereof is adjusted. In this case, in order to compensate the change inthickness, though the thickness of the first fitting sheet 125 may onlybe adjusted, the thickness of the first composite green sheet as a wholemay be adjusted. Otherwise, as shown in FIG. 43, the thickness of theportion of the shrinkage suppression green sheet 122 corresponding tothe cavity may be adjusted. In this case, the shrinkage suppressiongreen sheet 122 shown in FIG. 43 comprises a lamination of a thinshrinkage suppression green sheet 122 a and a shrinkage suppressiongreen sheet 122 b having a through hole at a cavity formation portionthereof and having a ceramic green sheet fitted in the through hole.With this, shrinkage suppression of the multilayer body as a whole andshrinkage suppression of the cavity bottom can independently becontrolled.

In the shrinkage suppression green sheet 122 b, the shape of the ceramicgreen sheet to be fitted (shape of the through hole) may not be the sameas the cavity shape, but is determined in view of the balance of theshrinkage compression forces. The thickness of each of the first fittingsheet 125 and the shrinkage suppression green sheets 122 a and 122 b mayappropriately be set similarly in consideration of the balance of theshrinkage suppression forces. A burnable sheet in place of the ceramicgreen sheet may be fitted in the through hole of the shrinkagesuppression green sheet 122 b. By setting the thickness of the ceramicgreen sheet or burnable sheet to conform to the thickness of theshrinkage suppression green sheet 122 b, uniform pressure can be appliedto the multilayer ceramic substrate in the pressing step.

The tenth embodiment of the present invention is directed to use of aburnable sheet when producing the multilayer ceramic substrate 101 shownin FIG. 21. FIG. 44 shows the fundamental production process in thisembodiment that mainly comprises the steps of laminating and pressinggreen sheets and shrinkage suppressing green sheets that constituteceramic layers after being fired, firing the pressed body, removingfired embedded green sheet body and removing fired shrinkage suppressiongreen sheets.

In fabricating a multilayer ceramic substrate, as shown in FIG. 44( a),a plurality of ceramic green sheets are laminated as green sheets for asubstrate in accordance with the number of the ceramic layersconstituting a multilayer ceramic substrate. Here, nine ceramic greensheets 161 to 169 are laminated. Each of the ceramic green sheets 161 to169 is formed through the steps of mixing ceramic powder, an organicbinder and an organic solvent to form dielectric paste in the form ofslurry, for example, and allowing the paste to grow on a PET sheet ofsupport, for example, in accordance with the doctor blade method. Any ofknown ceramic powder and organic vehicles (organic binder and organicsolvent) is usable in the present embodiment.

Of the ceramic green sheets 161 to 169, the two lower ceramic greensheets 161 and 162 are not required to form a cavity formation throughhole therein, but formed as ordinary flat green sheets. Of the twoceramic green sheets 161 and 162, the upper ceramic green sheet 162constitutes the cavity bottom.

On the ceramic green sheet 162, laminated are the seven remainingceramic green sheets 163 to 169 given through holes 163 a and 164 a of aprescribed shape corresponding to the opening shape of the cavity 111and cuts 165 a to 169 a to form separate portions 163 b to 169 b thatcorrespond to the cavity space. Thus, the seven ceramic green sheets 163to 169 correspond to the cavity formation green sheets.

In the present embodiment, the portions 165 b to 169 b separated by thecuts 165 a to 169 a exclusive of the ceramic green sheet 163 in contactwith the ceramic green sheet 162 constituting the cavity bottom and theceramic green sheet 164 thereon are utilized as embedded green sheets.However, this is not limitative. A separately formed embedded greensheet may be fitted in the through holes corresponding to the cavityformed in the ceramic green sheets 165 to 169. From the standpoint ofproductivity, however, utilization of the portions 165 b to 169 bseparated by the cuts 165 a to 169 a as embedded green sheets isadvantageous.

The ceramic green sheet 163 in contact with the ceramic green sheet 162constituting the cavity bottom has its portion corresponding to thecavity removed therefrom to form a through hole 163 a, and a shrinkagesuppression green sheet piece 170 a having a shape corresponding to thethrough hole 163 a is fitted and buried in the through hole.

The shrinkage suppression green sheet piece 170 a is obtained by beingpunched out so as to have a shape substantially conforming to the shapeof the through hole 163 a. The punching-out of the shrinkage suppressiongreen sheet can be performed in the same manner as in the sixthembodiment, for example. The shrinkage suppression green sheet piece 170a is formed of a material not shrunk at the firing temperature of theceramic green sheets 161 to 169, such as tridymite or cristobalite, orof a composition containing quartz, molten quartz, alumina, mullitezirconia, aluminum nitride, boron nitride, magnesium oxide, siliconcarbide, etc. The shrinkage suppression green sheet piece 170 a isdisposed in contact with the ceramic green sheet (ceramic green sheet162 in this case). The firing step is performed under these conditionsto suppress shrinkage of the ceramic green sheet 162 in the in-planedirection.

The ceramic green sheet 164 in contact with the ceramic green sheet 163has its portion corresponding to the cavity removed therefrom to form athrough hole 164 a, and a burnable sheet piece 171 a and a shrinkagesuppression green sheet piece 172 a each having a shape corresponding tothe through hole 164 a are fitted and buried in the through hole. Thisis shown in detail in FIG. 45.

As shown in FIG. 45( a), a ceramic green sheet 164 is formed and, asshown in FIG. 45( b), the portion of the ceramic green sheetcorresponding to the cavity is punched out to form a through hole 164 a.As shown in FIG. 45( c), a ceramic green sheet 172 is formed and, asshown in FIG. 45( d), a ceramic green sheet piece 170 a punched out soas to have a shape substantially conforming to the shape of the throughhole is formed. Similarly, as shown in FIG. 45( e), a burnable sheet 171is formed and, as shown in FIG. 45( f), it is punched out to form aburnable sheet piece 171 a having a shape substantially conforming tothe through hole 164 a. Subsequently, as shown in FIG. 45( g), theburnable sheet piece 171 a and shrinkage suppression green sheet piece172 a are fitted in the order mentioned and buried in the through hole164 a. Preferably, the total thickness of burnable sheet piece 171 a andshrinkage suppression green sheet piece 172 a conforms substantially tothe thickness of the ceramic green sheet 164.

In the present embodiment, it is necessary to pay attention to the sizesof the through hole 163 a, shrinkage suppression green sheet 170 a,through hole 164 a and cuts 165 a to 169 a. Specifically, when theceramic green sheets 163 to 169 have been laminated on the ceramic greensheet 162 constituting the bottom of the cavity, at at-least the portionwhere the conductive pattern 112 is disposed, the shapes of therespective through holes and cuts are controlled so that the end face ofthe shrinkage suppression green sheet piece 170 a (wall surface of thethrough hole 163 a of the ceramic green sheet 163) may be positionedoutside the end faces of the ceramic green sheet piece 172 a and theportions 165 b to 169 b separated by the cuts 165 a to 169 a.

The burnable sheet 171 (burnable sheet piece 171 a) is formed of amaterial burnt down at the firing temperature of the ceramic greensheets 161 to 169, such as a resin material. Particularly preferably,the organic binder contained in the ceramic green sheets 161 to 169 isused as the material for the burnable sheet 171 (burnable sheet piece171 a). By so doing, the burnable sheet 171 (burnable sheet piece 171 a)is burnt down with exactitude in the firing step. While the burnablesheet piece 117 a may be formed through punching the burnable sheet outas described above, it may be formed by the printing method, etc.

The multilayer body having these sheets laminated is in a state shown inFIG. 44( a), in which the shrinkage suppression green sheets 173 and 174are laminated, respectively, on the opposite surfaces of the multilayerbody having the plural ceramic green sheets 161 to 169 laminated,thereby suppressing shrinkage of the entire multilayer body in thein-plane direction. On the surface of the ceramic green sheet 162, theconductive pattern 112 is disposed as straddling the periphery of thecavity bottom. In addition, the shrinkage suppression green sheet piece170 a disposed in the through hole 163 a of the ceramic green sheet 163is in contact with the region of the ceramic green sheet 162constituting the cavity bottom, thereby suppressing shrinkage of thisportion in the in-plane direction.

Though the space corresponding to the cavity is ordinarily formed as aspace (concave) at this stage, in the production method of thisembodiment, the ceramic green sheet piece 172 a, portions 165 b to 169 bseparated by the cuts 165 a to 169 a and embedded ceramic green sheetpiece 175 are disposed as the embedded green sheets. When seeing theentire shape of the multilayer body, the multilayer body is formed asthat flat without any concave.

The multilayer body having the ceramic green sheets 161 to 169 andshrinkage suppression green sheets 173 and 174 laminated is to bepressed in the pressing step preparatory to the firing step. At thistime, when the multilayer body is formed with a concave corresponding tothe cavity, the concave will possibly collapse to deform the opening ofthe cavity. In the present embodiment, however, since the multilayerbody fabricated is uniform in thickness in the lamination direction andflattened over the entire thereof inclusive of the cavity portion owingto the presence of embedded green sheets, an ordinary flat mold die canbe used to press the multilayer body. Thus, the pressing step can beperformed with a simple means. While pressure is applied with themultilayer body sandwiched between the flat mold dies, as describedabove, the multilayer body coated with waterproof resin, etc. may besubjected to isostatic pressing.

After the firing step subsequent to the pressing step, as shown in FIG.44( b), the ceramic green sheets 161 to 169 are converted to ceramiclayers 102 to 110. At the time of firing, since the ceramic green sheets161 to 169 bound by the shrinkage suppression green sheets 173 and 174laminated thereon, they are shrunk only in the width direction and areseldom shrunk in the in-plane direction. The ceramic green sheet 162exposed to the cavity bottom is also suppressed from being shrunk in thein-plane direction.

In addition, the burnable sheet piece 171 a intervening between theembedded green sheets (ceramic green sheet piece 172 a, portions 164 bto 169 b of the ceramic green sheets 164 to 169 separated by the cuts164 a to 169 a and embedded ceramic green sheet piece 175) and theshrinkage suppression green sheet piece 170 a is burnt down before theceramic green sheets 161 to 169 are sintered. As a result, the bindingforce of the shrinkage suppressing green sheet piece 170 a disposed onthe cavity bottom is not exerted on the embedded green sheets to shrinkthe embedded green sheets in the in-plane direction. A fired body 176protrudes from the fired multilayer body as shown in FIG. 44( b) becausethe shrinkage in the thickness direction is small. Since the bindingforce is not exerted, as described above, the embedded green sheets areshrunk and consequently no stress is applied to the shrinkagesuppression green sheet piece 170 a and also to the ceramic green sheet162 immediately under it. The flatness of the ceramic layer 103 formedas a consequence of firing of the ceramic green sheet 162 is notdeteriorated.

Upon completion of the firing, the fired body 176 of the embedded greensheets is removed from the cavity space as shown in FIG. 44( c). Thefired body is separated from the shrinkage suppression green sheet piece170 a because the burnable sheet piece 171 a is burnt down and,therefore, can easily be removed by, for example, turning the firedmultilayer body upside down.

Finally, residuals 177 of the fired shrinkage suppression green sheets173 and 174 and the fired shrinkage suppression green sheet piece 170 aare removed to complete a multilayer substrate 101 having a cavity 111as shown in FIG. 44( d). The residuals 176 can be removed with ease bysome sort of cleaning step. The removal can be attained by stimulus of adegree by ultrasonic cleaning, for example. Thus, as the cleaning step,the step of ultrasonic cleaning in a solvent will suffice. Whenalumina-based green sheets are used as the shrinkage suppressing greensheets, however, the residuals 176 do not exfoliate spontaneously.Therefore, the residuals 76 are to be removed through polishing andcleaning by a wet blasting step.

The multilayer ceramic substrate 101 thus fabricated is excellent indimensional accuracy and in flatness of the cavity bottom and has nodeformation, such as by collapse of the cavity opening or bulgeformation around the cavity opening. Furthermore, since the shrinkage ofthe lower end of the sidewall of the cavity 111 is suppressed,disconnection of the conductive pattern 112 otherwise made by theshrinkage can be suppressed.

The eleventh embodiment of the present invention is directed to theapplication of burnable sheets to a production method of a multilayerceramic substrate having a cavity of multistage structure (two-stepstructure). FIG. 46 shows this embodiment. As shown in FIG. 46( a),shrinkage suppression green sheets 182 and 183 are laminated on theopposite surfaces of a multilayer body 181 of ceramic green sheets, andshrinkage suppression green sheet pieces 184 and 185 and burnable sheetpieces 186 and 187 are disposed respectively on the cavity bottom andstep bottom, with embedded green sheet 188 filled in the cavity. Themultilayer body in this state is subjected to pressing and firing steps.Also in this embodiment, since flatness of the multilayer body ismaintained, the pressing step is easy to perform. This embodiment doesnot adopt the step of compensating the embedded green sheet 188corresponding to the sheet on which the burnable sheet 187 is disposedto have a small thickness.

After the firing step, as shown in FIG. 46( b), a fired boy 189 ofembedded green sheets protrudes from a fired multilayer body and caneasily be removed such as by turning the fired multiplayer body upsidedown. A multilayer ceramic substrate 190 obtained is as shown in FIG.46( c) and is excellent in dimensional accuracy as a whole and,furthermore, the bottom 191 a and step surface 191 b of the cavity 111are excellent in dimensional accuracy and flatness. Moreover,disconnection of a conductive pattern 152 accompanied by the shrinkageof the region around the cavity in the surface direction can besuppressed. In the cavity of two-step structure, an electronic device ismounted on the bottom 191 a, and the conductive pattern connected to theelectronic device with bonding wires is provided on the step surface 191b.

The twelfth embodiment of the present invention adopts the dispositionof the first cavity formation ceramic layers and second cavity formationceramic layers having through holes of the same shape in which a layeris shifted so that the through holes partially overlap each other. Inthe sixth to eleventh embodiments, the opening area of the through holesin the first cavity formation ceramic layers has been made larger thanthat of the second cavity formation layers. In the present embodiment,however, at at-least part of the periphery of the cavity bottomoverlapping a conductive pattern, insofar as the through hole wallsurface of the first cavity formation ceramic layer is disposed outsidethe through hole wall surface of the second cavity formation ceramiclayer, the dimensional relationship and shapes of the through holes canbe made arbitrary.

A multilayer ceramic substrate of the present embodiment will bedescribed citing a multilayer ceramic substrate 201 shown in FIGS. 47(a) and 47(b) in which a conductive pattern 112 is disposed on only oneside of the periphery of the bottom 111 a of a square cavity 111 asstraddling the one side.

In producing the multilayer ceramic substrate 201, as shown in FIG. 48,a first composite green sheet 211 (first cavity formation green sheet)is formed in the composite green sheet formation step S12 so that theshape of a first fitting sheet 212 (shrinkage suppression sheet piece)may conform to the shape of the inside portion (embedded green sheet)130 a of the cut in a cut formation sheet 130 laminated thereon.

In the laminating step S16, a shrinkage suppression green sheet 122,ceramic green sheet 121, cavity bottom formation green sheet 132, firstcomposite green sheet 211, plural cut formation sheets 130 and uppermostcomposite green sheet 129 are laminated in the order mentioned to obtaina multilayer body. At this time, the first composite green sheet 211 andthe cut formation green sheet 130 are laminated to the effect that thefirst fitting sheet 212 and the embedded green sheet 130 a disposedimmediately thereon are shifted to have an overlapping portion so thatthe end face of the first fitting sheet 212 (shrinkage suppression greensheet piece) may be disposed outside the end face of the inside portion(embedded green sheet) 130 a of the cut in the cut formation green sheet130 laminated immediately thereon at at-least the portion of the firstfitting sheet 212 overlapping a conductive pattern 112.

Thereafter, the firing step S2, cavity formation step S3 and shrinkagesuppressing sheet removal step S4 are taken in the same manner as in thesixth embodiment. In the multilayer ceramic substrate 201 obtained, thethrough hole 202 a of the ceramic layer 202 has the same shape as thethrough hole 105 a of the ceramic layer 105 and, at the same time, thethrough holes 202 a and 105 a are disposed as shifted from each other ina partially overlapped fashion. Thus, the state is realized in which thewall surface of the through hole 202 a of the ceramic layer 202 at theportion corresponding to the conductive pattern 112 is positionedoutside the wall surface of the through hole 105 a of the ceramic layer105.

The thirteenth embodiment of the present invention is directed to amultilayer ceramic substrate having on the surface of a conductivepattern of the portions corresponding to the periphery of the cavitybottom a softening layer that gets soft at the firing temperature in thefiring step.

FIG. 49( a) to FIG. 49( d) show the simplest model of a multilayerceramic substrate 401 having a cavity 411 and comprising plural (ninehere) ceramic layers 402 to 410 stacked and integrated. Of the ceramiclayers 402 to 410, two lower layers 402 and 403 are flat ceramic layersprovided with no through hole for formation of a cavity. Of these, theupper ceramic layer 403 corresponds to a cavity bottom formation ceramiclayer, and part of the upper surface thereof is exposed to the bottomportion of the cavity 411 to constitute a bottom 411 a of the cavity.

The remaining ceramic layers 404 to 410 stacked on the ceramic layer 403are formed with through holes 404 a to 410 a, respectively, for definingthe sidewall of the cavity 411 and correspond to cavity formationceramic layers. The bottom 411 a constituted by the ceramic layer 403and the sidewalls of the through holes 404 a to 410 a of the ceramiclayers 404 to 410 made contiguous define the cavity 411 as a prescribedspace. The shape of the opening of the cavity is the same as that of thefirst embodiment.

A conductive pattern 412 is formed on the surface of the ceramic layer403 as straddling the periphery of the bottom 411 a of the cavity 411and has one end thereof exposed to the bottom 411 a of the cavity 411and connected to an electronic device to be accommodated within thecavity 411. The other end of the conductive pattern 412 is disposedbetween the ceramic layers 403 and 404 and connected to an internalelectrode or wiring formed inside the multilayer ceramic substrate 411.FIG. 49 shows the case where on each of the two opposed sides of thesquare cavity seen from top two strips of conductive patterns 412, i.e.four in total, are provided. The number and shape of the conductivepatterns are made optional. There is a case where the bottom 411 a ofthe cavity 411 is provided with a via hole for heat radiation.

In the multilayer ceramic substrate 401 of the present embodiment, atleast on the surfaces of the conductive patterns 412 of the portioncorresponding to the periphery of the bottom of the cavity 411, asoftening layer 413 is disposed. The softening layers 413 shown in FIG.46 rim in the form of a strap the two sides on which the conductivepatterns are disposed.

The softening layer 413 is formed of a material that gets soft at afiring temperature used for obtaining a multilayer ceramic substrate 401through the steps of lamination, pressing and firing of various kinds ofceramic green sheets. The interposition of the softened layer betweenthe conductive pattern 412 and the cavity formation and cavity bottomformation green sheets that become the cavity formation ceramic layers404 to 410 in the firing step enables stress applied to the ceramiclayer and conductive layer by the shrinkage of the cavity formationgreen sheets to be alleviated, thereby suppressing disconnection of theconductive pattern 412.

The softening layer is formed of a material required to get soft at thefiring temperature in the firing step for obtaining a multilayer ceramicsubstrate 401 and preferably not reacting with the ceramic layers. Asthe material, for example, glass can be used. Particularly, use of theglass of the same kind of glass contained in the ceramic layers 402 to410 is preferred. Examples thereof include borosilicate glass, bariumborosilicate glass, strontium borosilicate glass, zinc borosilicateglass and potassium borosilicate glass.

It is desirable that the width of the softening layer 413 outside thecavity 411 be so secured as to suppress disconnection of the conductivepattern 412. Specifically, the distance A1 between the periphery of thebottom 411 a of the cavity 411 and the outside edge of the softeninglayer is preferably in the range of 0.1 mm to 0.5 mm.

The width of the softening layer 413 inside the cavity 411 is desired tobe as small as possible from the standpoint of securing the flatness ofthe bottom 411 a of the cavity 411 in the ceramic layer 403. To beconcrete, the distance A2 between the periphery of the bottom 411 a ofthe cavity 411 and the inside edge of the softening layer 413 can be setto 0.5 mm or less (excluding 0 mm), for example. In order to reliablysuppress disconnection of the conductive pattern 412, the distance A2 ispreferably in the range of 0.05 mm to 0.5 mm and more preferably in therange of 0.1 mm to 0.5 mm.

The thickness of the softening layer 413 is too small to possibly allowthe effect of suppressing disconnection of the conductive pattern 412 tobecome insufficient and too large to possibly interfere with thelamination of the substrate green sheets.

A multilayer ceramic substrate fabricated by each production methoddescribed later has a cavity of a specific shape. Specifically as istypically shown in FIG. 50, the opening area of the inside is largerthan that of the opening close immediately to the shrinkage compressiongreen sheet to form a drum-shaped cavity.

The description on this point will be given in more detail. In thecavity 411, the opening dimension W1 at an opening 411 b is smaller thanthe opening dimension W2 at a position midway in the depth direction ofthe cavity 411. In other words, the opening area at the opening 411 b ofthe cavity 411 is smaller than the opening area at the position 411 cmidway in the depth direction of the cavity 411. In this example, theopening area of the cavity 411 is gradually increased up to the position411 c midway in the depth direction of the cavity and then graduallydecreased and, thus, the inner wall of the cavity 411 assumes asubstantially circular arc in cross section. Thus, the portion of thecavity midway in the depth direction is bulged out to shape adrum-shaped cavity.

The multilayer ceramic substrate 401 having the cavity 411 of the shapedescribed above has a great merit in terms of reliability owing to itsshape specificity. As shown in FIG. 51, for example, when an electronicdevice 440 is mounted within the cavity 411 and sealed with a resin J,the opening dimension at the opening 411 b of the cavity 411 is smallerthan that of the cavity inside, the resin J filled in the cavity willnot fall off at all. As described earlier, in the seal with the resin Jrelative to the conventional shape, the problem will arise in that theresin sealed exfoliates and falls off, resulting from the difference inthermal expansion coefficient between the ceramic layers 402 to 410constituting the multilayer ceramic substrate 401 and the resin J usedfor the seal. This problem becomes conspicuous particularly when atemperature change is repeated over a long period of time. In themultilayer ceramic substrate 401, since the opening area at the opening411 b of the cavity 411 is smaller than the opening area of the portionat the position 411 c midway in the depth direction of the cavity 411,the resin J filled and hardened in the cavity 411 cannot pass throughthe opening 411 b of the cavity 411 because of the larger area of theinside of the cavity and is retained within the cavity 411.

The multilayer ceramic substrate 401 having the configuration describedabove is formed through the production process performed. The productionprocess of the multilayer ceramic substrate in the present embodimentwill be described.

Also in the present embodiment, the non-shrinkage firing process isadopted, and the pressing and firing steps are performed, with theembedded green sheet disposed in a space corresponding to the cavity toeliminate collapse etc. at the pressing step in the same manner as inthe first embodiment. The step flowchart in the production process ispursuant to that shown in FIG. 2.

To be specific, in the green sheet formation step (S11) shown in FIG. 2,a ceramic green sheet (green sheet for a substrate) 421 shown in FIG.52( a) and a shrinkage suppression green sheet 422 shown in FIG. 52( b)are formed. Generally, these sheets 421 and 422 are formed as being inintimate contact with the surface of a support 423 that is a plasticsheet etc. The method of formation of the sheets 421 and 422 is the sameas that in the first embodiment.

After the fabrication of the ceramic green sheet 421 and shrinkagesuppression green sheet 422, a composite green sheet (green sheetcombining the ceramic green sheet with the shrinkage suppression greensheet) is fabricated utilizing the two sheets in the composite greensheet formation step (S12). The composite green sheet fabricated herecomprises a first composite green sheet 426 laminated immediately on thegreen sheet for formation of the cavity bottom and an uppermostcomposite green sheet laminated as an uppermost shrinkage suppressiongreen sheet. To fabricate the first composite green sheet 426, as shownin FIG. 53( a), first, the ceramic green sheet 421 produced in the greensheet formation step (S11) is formed with a first through hole 424.

The shrinkage suppression sheet 422 produced in the green sheetformation step (S11) is placed on the support 423 and cut into the sameshape as the first through hole 424 to obtain a first fitting sheet 425(corresponding to the shrinkage suppression green sheet piece). The cutfirst fitting sheet 425 is fitted in the first through hole 424 to forma first composite green sheet 426. At this time, in order to make thefirst composite green sheet 426 flat, preferably, the thickness of theceramic green sheet 421 is the same as that of the first fitting sheet425.

An uppermost composite green sheet 429 is produced in accordance withthe same production method as that of the first composite green sheet426. In the uppermost composite green sheet 429, as shown in FIG. 53(b), the shrinkage suppression green sheet 422 is formed with a throughhole in which a ceramic green sheet piece is fitted. To be specific, theshrinkage suppression green sheet 422 produced in the green sheetformation step (S11) is formed with a second through hole 427corresponding to the opening of the cavity. The production method of thesecond through hole 427 is the same as that of the first through hole424. The ceramic green sheet 421 produced in the green sheet formationstep (S11) is placed on the support 423 and cut into the same shape asthe second through hole 427 to obtain a second fitting sheet 428. Thecut second fitting sheet 428 is fitted in the second through hole 427,and the resultant composite sheet is allowed to exfoliate from thesupport 423 to form an uppermost composite green sheet 429. Also in thiscase, in order to make the uppermost composite green sheet 429 flat,preferably, the thickness of the shrinkage suppression green sheet 422is the same as that of the second fitting sheet 428.

In the cut formation step (S13), the ceramic green sheet 421 is formedwith a cut to be used as a cavity formation green sheet. Specifically,in the cut formation step (S13), the ceramic green sheet 421 produced inthe green sheet formation step (S11) is formed with a cut (or adiscontinuous portion) 431 to form a cut formation sheet 430 as shown inFIG. 54. The cut 431 indicates the discontinuous portion pierced in thedirection of the thickness of the ceramic green sheet 421. Incidentally,the discontinuous portion includes what is not pierced in the sheetwidth direction. The cut 431 is formed at the same position and in thesame shape as the first through hole 424 to overlap the first throughhole 424 when the first composite green sheet 426 previously preparedhas overlapped the cut formation sheet 430. The cut 431 may be formed bypunching out a predetermined portion of the ceramic green sheet 421,with the ceramic green sheet 421 in intimate contact with the surface ofthe support 423, with a die of a puncher or using a laser beam or with amicrodrill or by punching.

In the cut formation step (S13), the cut may be inserted into theceramic green sheets 421 one by one or together in a lump. In eithercase, in the cut formation sheets 430, the inside portions 430 aseparated by the cuts 431 are left intact and utilized as embedded greensheets in the laminating and firing steps.

The first composite green sheet 426, cut formation sheets 430 (cavityformation green sheets) and ceramic green sheet constituting the bottomof the cavity (cavity bottom formation green sheet) that are ceramicgreen sheets constituting the ceramic layers of a multilayer ceramicsubstrate after being fired (hereinafter referred to collectively as“dielectric layer sheets”) are provided with a via hole, via electrode,internal electrode pattern, etc. Via electrode paste is filled andsolidified by the stopgap printing, for example, to form a viaelectrode. Internal electrode paste is applied onto the ceramic greensheet, for example, in a prescribed pattern by the screen printing toform an internal electrode pattern.

Specifically, in the via hole formation step (S14), a via hole forforming a via electrode therein is formed in the dielectric layer sheet.In the conductor-printing step (S15), conductive paste is filled in thevia hole formed in the via hole formation step (S14) to form a viaelectrode. Also in the conductor-printing step (S15), an internalelectrode pattern is printed in a prescribed pattern on the surface ofthe dielectric layer sheet. In the conductor-printing step (S15), aninternal electrode pattern (conductive pattern) is formed on the surfaceof the substrate green sheet. As shown in FIG. 55, for example,conductive patterns 412 are formed on the surface of the ceramic greensheet 421 as straddling the periphery (shown by dashed line in FIG. 55)of the region constituting the bottom 411 a of the cavity 411.

In the softening layer formation step, a softening layer 413 is formedon part of the substrate green sheets having the conductive patterns 412formed in the conductor-printing step (S15). The softening layer 413 isformed at least on the surfaces of the conductive patterns 412 of theportion corresponding to the periphery of the bottom 411 a of the cavity411 in the multilayer ceramic substrate 401 fired. In FIG. 55, thesoftening layers 413 rim the two sides of the periphery (shown by dashedline) of the region constituting the bottom of the cavity 411 afterbeing fired, on which sides the conductive patterns 412 are disposed.

The softening layer 413 may be formed of any material that gets soft atthe firing temperature at which the firing step (S2) described later isperformed. It is also important that the material of the softening layer413 does not adversely affect the conductive pattern 412 and substrategreen sheet. As the favorable material, glass can be cited. Use of thesame glass as contained in the substrate green sheets as the softeninglayer 413 is most preferable.

After the via electrode or internal electrode pattern is formed on eachdielectric layer sheet and the softening layer 413 is formed, the thusfabricated sheets are laminated in the laminating step (S16) to form amultilayer body 433. The configuration of the multilayer body from thelaminating step (S16) to the shrinkage suppression sheet removal step(S4) is shown in FIG. 56( a) to FIG. 56( d). Incidentally, the stepshown in FIG. 56( c) and the step shown in FIG. 56( d) may be performedinversely or simultaneously.

In the laminating step (S16), as shown in FIG. 56( a), a shrinkagesuppression green sheet 422, ceramic green sheet 421, cavity bottomformation green sheet 432, first composite green sheet 426, cutformation sheet 430 and uppermost composite green sheet 429 arelaminated in the order mentioned from the lowermost layer.

After the laminating step (S16), the pressing step (S17) is performed.The pressing step (S17) is a press-on step for the multilayer body 433produced in the laminating step (S16). The press-on step is performed,with the multilayer body placed in an ordinary die having upper andlower flat punches. The preferable conditions of the press-on stepinclude a pressure of 30 to 80 MPa and a period of around 10 minutes. Inthe present embodiment, since the uppermost and lowermost layers of themultilayer body 433 are flat and further since the portion 430 aseparated by the cut 431 is left intact and filled in the portion wherethe cavity is formed, pressure in the pressing step can be applieduniformly. Therefore, there is no case where the opening of the cavityis deformed by collapse or damaged by the pressure applied as in theprior art.

The firing step (S2) is then performed, in which the multilayer body 433pressed on in the pressing step (S17) is fired. The multilayer body 433is subjected to debinder treatment before the firing step. Theconditions of the debinder treatment may be generally adopted ones. Thefiring step is then performed to form a fired multilayer body 434. Theatmosphere in the firing step is not particularly restricted. When abase metal, such as nickel or nickel alloy, is used for the viaelectrode and internal electrode pattern, the atmosphere is preferred tobe a reduction atmosphere. The firing temperature is preferred to be inthe range of 800° C. to 1000° C. As a consequence, the conductivematerial and resistance material can be fired at the same time, and themultilayer ceramic substrate subsequently obtained can be used for LTCCmodules including high-frequency superposed modules, antenna switchmodules, filter modules, etc.

In the fired multilayer body 434 having undergone the firing step (S2),as shown in FIG. 56( b), the portion 430 a of the cut formation sheet430 inside the cut 431 projects from the cavity. The reason therefor isas follows. When the multilayer body 433 is fired, the ceramic greensheet 421, cavity bottom formation sheet 432, first composite greensheet 426 and cut formation sheet 430 that are the dielectric layersheets are sintered and intended to shrink. At this time, the ceramicgreen sheet 421 is in intimate contact with the lower shrinkagesuppression green sheet 422. Since the shrinkage suppression green sheet422 does not shrink at the firing temperature of the dielectric layersheets, as described earlier, the shrinkage of the ceramic green sheet421 in the plane surface direction is suppressed. Since the portion 430b of the cut formation sheet 430 outside the cut 431 is in intimatecontact with the uppermost composite green sheet 429, the shrinkagethereof is also suppressed. In addition, since the cavity bottomformation green sheet 432 is in intimate contact with the first fittingsheet 425 of the first composite green sheet 426 at the cavity bottom,the shrinkage thereof is similarly suppressed.

On the other hand, the portion 430 a of the cut formation sheet 430inside the cut 431 is not provided on the upper side thereof with ashrinkage suppression sheet, the shrinkage thereof is not suppressed.Thus, the inside portion 430 a of the cut 431 is shrunk in the planesurface direction to separate from the outside portion 430 b of the cut431. The degree of this shrinkage is larger toward the upper layer fromthe first fitting sheet 425 on the cavity bottom, and the degree ofshrinkage in the thickness direction is made smaller by the amount ofthe inside portion 340 a of the cut 431 shrunk in the plane surfacedirection. Therefore, the first fitting sheet 425, second fitting sheet428 and the portion sandwiched between the two sheets (inside portion430 a of the cut 431) after being fired project from the surface of thefired multilayer body 434.

In the present embodiment, since the softening layer that has got softat the firing temperature at which the firing step (S2) is performed isinterposed between the conductive pattern 412 and the cavity formationgreen sheet constituting the lower end of the sidewall of the cavity 411a (ceramic green sheet 421 constituting the first composite sheet 426).When the cavity formation green sheet shrinks in the direction apartfrom the center of the cavity, therefore, it is moved as being slid onthe surface of the softening layer that has got soft. For this reason,the stress exerted on the conductive pattern 412 is alleviated tosuppress disconnection of the conductive pattern 412.

Of the periphery of the cavity bottom, since two sides on which noconductive pattern 412 exists have no softening layer 413, they aregreatly shrunk in the in-plane direction, but do not adversely affectthe conductive pattern 412 exposed to the cavity bottom.

As described earlier, the first fitting sheet 425, second fitting sheet428 and the portion sandwiched between the two sheets (inside portion430 a of the cut 431) are brought to the state of shrinkage differentfrom that of the portion 430 b of the ceramic green sheet 421 and cutformation sheet 430 outside the cut 431. For example, the portion 430 aof the cut formation sheet 430 inside the cut 431 is completelyseparated from the outside portion 30 b. Also at the cavity bottom, thefirst fitting 425 is made fragile by the firing and the binding force atthis portion becomes weak. As shown in FIG. 56( c), therefore, the firstfitting sheet 425, second fitting sheet 428 and the portion sandwichedbetween the two sheets (inside portion 430 a of the cut 431) filled inthe cavity are enabled to fall off with a slight stimulus. Even in thecase of the cavity having a complicated shape, the inside portion 430 aof the cut 431 is enabled to fall off. In order to cause the insideportion 430 a of the cut 431 to fall off, a small force may be exertedonto it.

Specifically, as shown in FIG. 56( c), the first fitting sheet 425,second fitting sheet 428 and the portion sandwiched between the twosheets (inside portion 430 a of the cut 431) are removed to form thecavity and, at the same time, the shrinkage compression sheet removalstep (S4) is performed when necessary. In the step (S4), the uppermostsheet 435 and the lowermost sheet 436 of the fired multilayer body 434(shrinkage compression green sheet 422 and uppermost composite greensheet 229 that have been fired) are removed. The removal methodcomprises subjecting the fired multilayer body 434 to ordinaryultrasonic washing in a solvent or wet blasting. When the shrinkagesuppression green sheet 422 is formed of a tridymite-silica-basedmaterial or cristobalite-silica-based material, since the major parts ofthe uppermost sheet 435 and lowermost sheet 436 after the firingexfoliate spontaneously, washing of the slightly remaining part willsuffice.

Besides the steps described above, a cutting step, a polishing step,etc. are performed as occasion demands to obtain the multilayer ceramicsubstrate 401 shown in FIG. 49. The cutting step includes division witha diamond scriber and, when the fired multilayer body is thick, cuttingby a dicing system. The polishing step is performed through the lappingprocess, for example. lapping process is a processing method for buffingthe object to be processed using a processed liquid containing abrasivecoating, with abrasive coating not contained in a rotary bed. Use of awet barrel is also available.

An electronic device 440 is mounted on the multilayer ceramic substrate401 produced. The state of the electronic device 440 mounted on thesubstrate is shown in FIG. 57. As shown in FIG. 57, the electronicdevice 440 is accommodated in the cavity 411 of the multilayer ceramicsubstrate 401. The backside of the electronic device 440 is connected tothe conductive patterns 412 exposed to the cavity bottom. The electronicdevice is further connected to electrodes (not shown) formed on themultilayer ceramic substrate 401 with bonding wires 441. The electrodesinclude surface electrodes and via electrodes printed on the surface ofthe multilayer ceramic substrate 401 and internal electrodes printedinside the multilayer ceramic substrate 401. The multilayer ceramicsubstrate thus fabricated by the method of the present embodimentpermits accommodation of an electronic device therein and satisfies thedemand of making the substrate small in size and height.

The fourteenth embodiment of the present invention is directed to asoftening layer formed so as to rim the entire periphery of the cavitybottom.

In the thirteenth embodiment, since there is no concern thatdisconnection of the conductive pattern 412 arises at the sides of theperiphery of the bottom 411 a of the cavity 411 on which no conductivepattern 412 exists, no softening layer exists on the sides. For thisreason, the bottom 411 a of the cavity 411 corresponding to the sides isstrongly bound by the first fitting sheet 425 and, as a result, a largestress is generated at the boundary between the bottom 411 a of thecavity 411 and the outside of the bottom. When an internal electrodepattern is interposed between the lower ceramic layers of the sidewallsof the cavity 411, for example, there is a possibility of the internalelectrode pattern being disconnected.

In the present embodiment, the shape of the softening layer 413 is inthe form of a frame, for example, to rim the entire periphery of thebottom of the cavity 411. As shown in FIG. 58, in the multilayer ceramicsubstrate 445 of the present embodiment, the softening layer 413 isdisposed on the entire periphery of the bottom of the cavity 411including the portion of the cavity 411 provided with no conductivepattern 412, i.e. along the lower end of the sidewall of the cavity 411.The softening layer 413 is disposed between the ceramic layers 403 and404.

To obtain the multilayer ceramic substrate 445 shown in FIG. 58, thesoftening layer 413 is formed so as to rim the entire periphery of theregion that becomes the bottom of the cavity 411 after being fired,thereby forming the bottom formation green sheet 432.

In the multilayer ceramic substrate 445, the softening layer 413 isformed also on the portion of the periphery of the bottom 411 a of thecavity 411 provided with no conductive pattern 412. In the portion ofthe periphery of the bottom 411 a of the cavity 411 provided with noconductive pattern 412, therefore, the softening layer 413 alleviatesthe stress exerted on the bottom formation green sheet, resulting insuppression of disconnection of the internal electrode pattern disposedon the lower portion of the sidewall of the cavity.

FIG. 59 shows an example in which conductive patterns 412 are providedon all sides of the periphery of the cavity 411 having a square opening.Also in this example, a softening layer 413 is formed to rim the entireperiphery of the bottom 411 a of the cavity 411. In the multilayerceramic substrate, as shown in FIG. 60, the conductive pattern 412 maybe formed on the entire bottom of the cavity. In either case,disconnection of the conductive pattern 412 exposed to the cavity bottomor the internal electrode pattern can reliably be suppressed.

The fifteenth embodiment of the present invention will now be described.The difference thereof from the thirteenth embodiment is to form thecavity into a multistage cavity (two-step cavity with two bottoms inthis case).

A multilayer ceramic substrate having a two-step cavity with two bottomswill be described hereinafter with reference to FIG. 61. The multilayerceramic substrate 450 shown in FIG. 61 has a cavity 451 with two bottomsand comprises plural (14 here) ceramic layers laminated and madeintegral. A ceramic layer 403 corresponds to the cavity bottom formationceramic layer and a part thereof is exposed to the cavity bottom toconstitute the deepest bottom 451 a of the cavity 451 with two bottoms.Of the ceramic layers constituting the multilayer ceramic substrate 450,the configuration of the ceramic layers 402 to 409 is substantially thesame as that of the thirteenth embodiment. Part of the ceramic layer 410constitutes a second-step bottom 451 a of the cavity 451 with twobottoms. Therefore, the ceramic layer 410 corresponds to a cavity bottomformation ceramic layer. The surface of the ceramic layer 410 isprovided thereon with a conductive pattern 452.

The ceramic layers 453 to 457 laminated on the ceramic layer 410 areprovided with through holes 453 a to 457 a and correspond to cavityformation ceramic layers. The sidewalls of the through holes 453 a to457 a of the ceramic layers 453 to 457 made contiguous define theshallower space of the two-step cavity 451.

The multilayer ceramic substrate 450 of the present embodiment, when aconductive pattern 452 is formed on the second bottom 451 b asstraddling the periphery of the bottom 451 b, a second softening layer458 is disposed at least on the surface of the conductive pattern 452 ofthe periphery of the bottom 451 b.

In fabricating the multilayer ceramic substrate of the presentembodiment, a first composite green sheet is disposed on the deepestbottom of the cavity, a second composite green sheet is disposed on thesecond bottom (step surface) and the cut formation sheets having throughholes different in size from each other to conform to the dimensions ofthe multistage cavity portions are laminated thereon.

FIG. 62 shows the detailed shape of the cavity of the multilayer ceramicsubstrate shown in FIG. 61. Here, in the sidewall of each of the cavityportions 451 c and 451 d, the shrinkage in the surface directiongradually increases with an increasing distance from the shrinkagesuppressing green sheet, and the opening size at each opening is smallerthan that at a position midway in the depth direction. In the cavityportion 451 c, when the opening size at the opening is denoted by W3 andthe opening size at a position midway in the depth direction by W4,W3<W4. Similarly, in the cavity portion 451 d, when the opening size atthe opening is denoted by W5 and the opening size at a position midwayin the depth direction by W6, W5<W6. The cross-sectional shape of thesidewall of each of the cavity portions 451 c and 451 d is a circulararc and, therefore, the shape of each of the cavity portions 451 c and451 d assumes a pot or urceolate shape.

The second and subsequent step cavity portions (cavity portion 451 dhere) do not always assume a pot or urceolate shape, but may be of ashape having the largest opening area and gradually reducing the openingarea toward the depth direction as shown in FIG. 63. In this case, whenthe opening size at the opening is set to be W5 and the opening size ata position midway in the depth direction to be W6, W5>W6. The first stepcavity portion 451 c assumes a pot or urceolate shape, whereas thesecond step cavity portion 451 d assumes a shape of bowl. By making thesecond and subsequent cavity portions bowl-shaped, wire bonding inmounting an electronic device on the cavity portion 451 d is ready toperform, thereby enabling efficient device mounting.

In the multistage cavity 451 of the multilayer ceramic substrate 450,since at least the first step cavity portion 451 c has a shape of a drumhaving the opening area larger at the inside than at the opening,reliable resin-seal in the cavity portions 451 c and 451 d can besecured.

A production method of the multilayer ceramic substrate 450 having theconfiguration described above will be described. The difference thereoffrom the thirteenth embodiment is to form the cavity into a multistagecavity (two-step cavity with two bottoms in this case). To be specific,the different points in step are to dispose a first composite greensheet on the deepest bottom of the cavity, dispose a second compositegreen sheet on the second step bottom (step surface) and laminate thecut formation sheets having through holes different in size from eachother.

In the present embodiment, a second composite green sheet 443 shown inFIG. 64( a) is formed in the composite green sheet formation step (S12).In producing the second composite green sheet 443, the ceramic greensheet 421 produced in the green sheet formation step (S11) is formedwith a third through hole 444 that overlaps the first through hole 424and is larger than the first through hole 424. The formation method ofthe third through hole 444 is the same as the formation method of thefirst through hole 424.

The shrinkage suppression green sheet 422 produced in the green sheetformation step (S11) is cut into substantially the same shape as thethird through hole 444 to form a third fitting sheet 445, which isfitted in the third through hole 444. In addition, the third fittingsheet 445 fitted is formed with a fourth through hole 446 formed at thesame position as the first through hole 424 to have substantially thesame shape as the first through hole, in which fourth through hole thesecond fitting sheet 428 obtained by cutting the ceramic green sheet 421into substantially the same shape as the fourth through hole 446 isfitted. A second composite green sheet 443 is thus produced.

In producing the second composite green sheet 443, a reverse procedureof first fitting the second fitting sheet 428 in the fourth through hole446 and then fitting the third fitting sheet 445 in the third throughhole 444 may be adopted.

In the present embodiment, as shown in FIG. 64( b), a cut formationsheet (second cut formation sheet 447) different from the cut formationsheet 430 in the thirteenth embodiment is formed in the cut formationstep (813). The difference between the second cut formation sheet 447and the previous cut formation sheet 430 is the size of a cut 448 thatis larger than that of the cut 431. To be specific, the cut 448 in thesecond cut formation sheet 447 is formed at the same position and insubstantially the same shape as the third through hole 444 of the secondcomposite green sheet 443.

In the conductor-printing step (S15), as shown in FIG. 65, conductivepatterns 452 are formed on the surface of the uppermost cut formationsheet 430 as straddling the periphery of the cavity bottom 451 b tofabricate a second cavity bottom formation green sheet 453. Theconductive patterns 412 are formed on the surface of the green sheet 421in the same manner as in the thirteenth embodiment to form a bottomformation green sheet 432.

In the softening layer formation step, as shown in FIG. 65, a secondsoftening layer 458 is formed to rim at least two sides, on which theconductive patterns 452 are formed, of the periphery (shown by dashedline) of the region constituting the second step bottom 451 b of thecavity 411.

An example of the multilayer body 454 having the sheets laminated in thepresent embodiment is shown in FIG. 66( a). The sheets constituting themultilayer body 454 are laminated in order from below. That is to say,the shrinkage suppression green sheet 422, ceramic green sheet 421,cavity bottom formation green sheet 432, first composite green sheet426, cut formation sheet 430, second cavity bottom formation green sheet453, second composite green sheet 443, second cut formation sheet 447and uppermost composite green sheet 429 are laminated in the ordermentioned from the lowermost layer. Incidentally, the number of each ofthe shrinkage suppression green sheet 422, cavity bottom formation greensheet 432, first composite green sheet 426, second cavity bottomformation green sheet 453, second composite green sheet 443 anduppermost composite green sheet 429 to be laminated is one. Of course,plural number of each of these sheets may be laminated. The number ofeach of the ceramic green sheet 421, cut formation sheet 430 and secondcut formation sheet 447 is determined depending on the interlayerelectrode pattern configuration required for the multilayer ceramicsubstrate and the size of an electronic device mounted on the inside ofthe substrate and is generally two or more. In this example, one ceramicgreen sheet 421, five cut formation sheets 430 and four second cutformation sheets 447 are laminated. Of course, the number of each ofthese sheets is not restricted to this example, but is optional. Themultilayer body 454 may also be formed with another cavity on the sideof the shrinkage suppression green sheet 422, for example, besides thecavity shown in FIG. 66( a).

When the multilayer body 454 has been fired, a fired multilayer body 455shown in FIG. 66( b) is obtained. In the fired multilayer body 455, theportion 456 a filled in the cavity is shrunk in the surface direction toproject from the cavity. The portion is removed in the same manner as inthe thirteenth embodiment and, when necessary, the shrinkage suppressionsheet removal step (S4) is performed to complete a multilayer ceramicsubstrate 450 having a two-step cavity 451 with two bottoms as shown inFIG. 61 (FIG. 62).

An example in which an electronic device 440 is mounted on themultilayer ceramic substrate 450 having the two-step cavity 451 with twobottoms is shown in FIG. 67. As shown in FIG. 67, the electronic device440 is accommodated in a lower cavity portion and connected to theconductive pattern 412 exposed to the deepest bottom 411 a. Theelectronic device 440 is also connected to the conductive pattern 452exposed to the bottom 451 b of the upper cavity portion with bondingwires 441. In this way, the multilayer ceramic substrate 450 fabricatedby the production method of the present embodiment enables both theelectronic device 440 and the bonding wires 441 to be accommodated inthe inside thereof. Thus, the bonding wires and the like do not protrudefrom the surface of the multilayer ceramic substrate. Also in amultilayer ceramic substrate provided therein with a plurality ofdielectric layers, an electronic device can be mounted at high densityto satisfy the demand of making the size and height small.

In addition, since the second softening layer 458 is disposed on thesurface of the conductive pattern 452 of the periphery of the secondstep bottom 451 b of the two-step cavity 451, concentration of stress tothe conductive pattern 452 when the lower end of the sidewalls of theceramic layers 453 to 457 is shrunk in the in-plane direction isalleviated to suppress disconnection of the conductive pattern 452.

By making use of the production method of a multilayer ceramic substrateaccording to the present embodiment, a multilayer ceramic substratehaving a three or more step cavity with three or more bottoms can befabricated. At this time, when a conductive pattern is formed asstraddling the periphery of a third step bottom, for example, asoftening layer is disposed at a prescribed position in the same manneras in the production process of the multilayer ceramic substrate havinga two-step cavity with two bottoms. With this, disconnection of theconductive pattern formed on the third step bottom.

In the production method of the thirteenth embodiment, for example,failure to achieve a balance of the upper and lower shrinkagesuppression forces depending on the layer structure of the multilayerceramic substrate will possibly deform the cavity bottom, as extremelydepicted in FIG. 68, for example. In such a case, the thickness of theshrinkage suppressing green sheets sandwiching the cavity bottom isadjusted to avoid the deformation. The sixteenth embodiment of thepresent invention is directed to this adjustment.

To be specific, as shown in FIG. 69, the thickness of the firstcomposite green sheet 426 having the shrinkage suppression green sheetpiece (first fitting sheet 425) fitted in the cavity formation portionthereof is adjusted. In this case, in order to compensate the change inthickness, though the thickness of the first fitting sheet 425 may onlybe adjusted, the thickness of the first composite green sheet as a wholemay be adjusted. Otherwise, as shown in FIG. 07, the thickness of theportion of the shrinkage suppression green sheet 422 corresponding tothe cavity may be adjusted. In this case, the shrinkage suppressiongreen sheet 422 shown in FIG. 70 comprises a lamination of a thinshrinkage suppression green sheet 422 a and a shrinkage suppressiongreen sheet 422 b having a through hole at a cavity formation portionthereof and having a ceramic green sheet fitted in the through hole.With this, shrinkage suppression of the multilayer body as a whole andshrinkage suppression of the cavity bottom can independently becontrolled.

In the shrinkage suppression green sheet 222 b, the shape of the ceramicgreen sheet to be fitted (shape of the through hole) may not be the sameas the cavity shape, but is determined in view of the balance of theshrinkage compression forces. The thickness of each of the first fittingsheet 425 and the shrinkage suppression green sheets 422 a and 422 b mayappropriately be set similarly in consideration of the balance of theshrinkage suppression forces. In addition, a burnable sheet in place ofthe ceramic green sheet may be fitted in the through hole of theshrinkage suppression green sheet 422 b. Also in this case, uniformpressure can be applied in the pressing step.

The seventeenth embodiment of the present invention is directed to useof a burnable sheet when producing the multilayer ceramic substrate 401shown in FIG. 49. FIG. 71 shows the fundamental production process inthis embodiment that mainly comprises the steps of laminating andpressing green sheets and shrinkage suppressing green sheets thatconstitute ceramic layers after being fired, firing the pressed body,removing fired embedded green sheet body and removing fired shrinkagesuppression green sheets.

In fabricating a multilayer ceramic substrate, as shown in FIG. 71( a),a plurality of ceramic green sheets are laminated as green sheets for asubstrate in accordance with the number of the ceramic layersconstituting a multilayer ceramic substrate. Here, nine ceramic greensheets 461 to 469 are laminated. Each of the ceramic green sheets 461 to469 is formed through the steps of mixing ceramic powder, an organicbinder and an organic solvent to form dielectric paste in the form ofslurry, for example, and allowing the paste to grow on a PET sheet ofsupport, for example, in accordance with the doctor blade method. Any ofknown ceramic powder and organic vehicles (organic binder and organicsolvent) is usable in the present embodiment.

Of the ceramic green sheets 461 to 469, the two lower ceramic greensheets 461 and 462 are not required to form a cavity formation throughhole therein, but formed as ordinary flat green sheets. Of the twoceramic green sheets 461 and 462, the upper ceramic green sheet 462corresponds to a cavity bottom formation green sheet constituting thecavity bottom.

On the ceramic green sheet 462, laminated are the seven remainingceramic green sheets 463 to 469 given a through hole 463 a and cuts 464a to 469 a of a prescribed shape corresponding to the opening shape ofthe cavity 411 to form separate portions 463 b to 469 b that correspondto the cavity space. Thus, the seven ceramic green sheets 463 to 469correspond to the cavity formation green sheets.

In the present embodiment, the portions 464 b to 469 b separated by thecuts 464 a to 469 a exclusive of the ceramic green sheet 463 in contactwith the ceramic green sheet 462 constituting the cavity bottom areutilized as embedded green sheets. However, this is not limitative. Aseparately formed embedded green sheet may be fitted in the throughholes corresponding to the cavity formed in the ceramic green sheets 464to 469. From the standpoint of productivity, however, utilization of theportions 464 b to 469 b separated by the cuts 464 a to 469 a as embeddedgreen sheets is, advantageous.

On the other hand, the ceramic green sheet 463 in contact with theceramic green sheet 462 constituting the cavity bottom has its portioncorresponding to the cavity removed therefrom to form a through hole 463a, and a shrinkage suppression green sheet piece 470 a having a shapecorresponding to the through hole 463 a and burnable sheet piece 471 aare fitted and filled in the through hole 463 a. This is shown in detailin FIG. 72.

As shown in FIG. 72( a), a ceramic green sheet 463 is formed and, asshown in FIG. 72( b), the portion of the ceramic green sheetcorresponding to the cavity is punched out to form a through hole 463 a.As shown in FIG. 72( c), a shrinkage suppression green sheet 470 isformed and, as shown in FIG. 72( d), a shrinkage suppression green sheetpiece 470 a punched out so as to have a shape substantially conformingto the shape of the through hole 463 a is formed. Similarly, as shown inFIG. 72( e), a burnable sheet 471 is formed and, as shown in FIG. 72(f), it is punched out to form a burnable sheet piece 471 a having ashape substantially conforming to the through hole 463 a. Subsequently,as shown in FIG. 72( g), the shrinkage suppression green sheet piece 470a and burnable sheet piece 471 a are fitted in the order mentioned andburied in the through hole 463 a of the ceramic green sheet 463.Preferably, the total thickness of the shrinkage suppression green sheetpiece 470 a and burnable sheet piece 471 a conforms substantially to thethickness of the ceramic green sheet 463.

The shrinkage suppression green sheet 470 (shrinkage suppression greensheet piece 470 a) is formed of a material not shrunk at the firingtemperature of the ceramic green sheets 461 to 469, such as tridymiteetc. The burnable sheet 471 (burnable sheet piece 471 a) is formed of amaterial burnt down at the firing temperature of the ceramic greensheets 461 to 469, such as a resin material.

As described above, the ceramic green sheets 461 to 469 are laminatedand, the shrinkage suppression green sheets 473 and 474 overlap thesurfaces of the outermost green sheets 461 and 469, respectively. Theshrinkage suppression green sheet 473 and 474 are formed of the samematerial as the aforementioned shrinkage suppression green sheet 470.The shrinkage suppression green sheet 474 disposed on the side of theceramic green sheet 469 formed with a through hole (by the cut 469 a)corresponding to the cavity is also formed with a through hole 474 acorresponding to the opening of the cavity, in which an embedded ceramicgreen sheet piece 475 separately punched out is fitted.

The multilayer body having these sheets laminated is in a state shown inFIG. 71( a), in which the shrinkage suppression green sheets 473 and 474are laminated, respectively, on the opposite surfaces of the multilayerbody having the plural ceramic green sheets 461 to 469 laminated,thereby suppressing shrinkage of the entire multilayer body in thein-plane direction. A conductive pattern 412 is disposed on the surfaceof the ceramic green sheet 462 as straddling the periphery of the cavitybottom. In addition, the shrinkage suppression green sheet piece 470 adisposed in the through hole 463 a of the ceramic green sheet 463 is incontact with the region of the ceramic green sheet 462 constituting thecavity bottom, thereby suppressing shrinkage of this portion in thein-plane direction.

Though the space corresponding to the cavity is ordinarily formed as aspace (concave) at this stage, in the production method in thisembodiment, the portions 464 b to 469 b separated by the cuts 464 a to469 a and the embedded ceramic green sheet piece 475 are disposed as theembedded green sheet. When seeing the entire shape of the multilayerbody, the multilayer body is formed as that flat without any concave.

The multilayer body having the ceramic green sheets 461 to 469 andshrinkage suppression green sheets 473 and 474 laminated is to bepressed in the pressing step preparatory to the firing step. At thistime, when the multilayer body is formed with a concave corresponding tothe cavity, the concave will possibly collapse to deform the opening ofthe cavity. In the present embodiment, however, since the multilayerbody fabricated is uniform in thickness in the lamination direction andflattened over the entire thereof inclusive of the cavity portion owingto the presence of embedded green sheets, an ordinary flat mold die canbe used to press the multilayer body. Thus, the pressing step can beperformed with a simple means. While pressure is applied with themultilayer body sandwiched between the flat mold dies, as describedabove, the multilayer body coated with waterproof resin, etc. may besubjected to isostatic pressing.

After the firing step subsequent to the pressing step, as shown in FIG.71( b), the ceramic green sheets 461 to 469 are converted to ceramiclayers 402 to 410. At the time of firing, since the ceramic green sheets461 to 469 bound by the shrinkage suppression green sheets 473 and 474laminated thereon, they are shrunk only in the width direction and areseldom shrunk in the in-plane direction. The ceramic green sheet 462exposed to the cavity bottom is also suppressed from being shrunk in thein-plane direction.

In addition, the burnable sheet piece 471 intervening between theembedded green sheets (portions 464 b to 469 b separated by the cuts 464a to 469 a from the ceramic green sheets 464 to 469 and embedded ceramicgreen sheet piece 475) filled in the cavity space and the shrinkagesuppression green sheet piece 470 a is burnt down before the ceramicgreen sheets 461 to 469 are sintered. As a result, the binding force ofthe shrinkage suppressing green sheet piece 470 a disposed on the cavitybottom is not exerted on the embedded green sheets to shrink theembedded green sheets in the in-plane direction. A fired body 476protrudes from the fired multilayer body as shown in FIG. 71( b) becausethe shrinkage in the thickness direction is small. Since the bindingforce is not exerted, as described above, the embedded green sheets areshrunk and consequently no stress is applied to the shrinkagesuppression green sheet piece 470 a and also to the ceramic green sheet462 immediately under it. The flatness of the ceramic layer 403 formedas a consequence of firing of the ceramic green sheet 462 is notdeteriorated.

Upon completion of the firing, the fired body 476 of the embedded greensheets is removed from the cavity space as shown in FIG. 71( c). Thefired body is separated from the shrinkage suppression green sheet piece470 a because the burnable sheet piece 471 a is burnt down and,therefore, can easily be removed by, for example, turning the firedmultilayer body upside down.

Finally, residuals 477 of the fired shrinkage suppression green sheets473 and 474 and the fired shrinkage suppression green sheet piece 470 aare removed to complete a multilayer substrate 401 having a cavity 411as shown in FIG. 71( d). The residuals 477 can be removed with ease bysome sort of cleaning step. The removal can be attained by stimulus of adegree by ultrasonic cleaning, for example. Thus, as the cleaning step,the step of ultrasonic cleaning in a solvent will suffice. Whenalumina-based green sheets are used as the shrinkage suppressing greensheets, however, the residuals 477 do not exfoliate spontaneously.Therefore, the residuals 477 are to be removed through polishing andcleaning by a wet blasting step.

The multilayer ceramic substrate 401 fabricated as described above isexcellent in dimensional accuracy and flatness of the cavity bottom, hasno deformation including collapse of the cavity opening and bulgesaround the cavity opening. Furthermore, the formation of the softeninglayer 413 in the multilayer ceramic substrate 401 suppressesdisconnection of the conductive pattern 412.

The eighteenth embodiment of the present invention is directed to use ofa burnable sheet on each of the bottoms of the cavity portions inproducing a multilayer ceramic substrate having a multistage cavity (ofa two-step structure) as shown in FIG. 73. In this case, as shown inFIG. 73( a), shrinkage suppression green sheets 482 and 483 arelaminated on the opposite surfaces of a multilayer body 481 of ceramicgreen sheets and, at the same time, shrinkage suppression green sheetpieces 484 and 485 and burnable sheet pieces 486 and 487 are disposed onboth the cavity bottom and stem bottom. The pressing step and firingstep are performed, with embedded green sheets 488 filled in the cavityspace of the two-step structure. Also in the present embodiment, theflatness of the multilayer body is secured, and the pressing step iseasy to perform.

Though a fired body 489 of the embedded green sheets after the firingstep protrudes form the multilayer body as shown in FIG. 73( b), it caneasily be removed by turning the multilayer body upside down in the samemanner as described above. A multilayer ceramic substrate 490 obtainedis as shown in FGI. 73(c) and is excellent in entire dimensionalaccuracy as well as in dimensional accuracy of the bottom 491 a andstepped surface 491 b of the cavity 491 and in their flatness. Inaddition, the softening layers 413 and 458 are disposed on the bottoms,respectively, to enable disconnection of the conductive patterns 412 and452 accompanied by shrinkage of the region around the cavity in thein-plane direction to be suppressed. Incidentally, in the case of thecavity 491 of the two-step structure, an electronic device is mounted onthe bottom 491 a and the stepped surface 91 b is provided thereon with aconductive pattern connected to the electronic device with bondingwires.

Concrete examples of the present invention will be described hereinafterbased on the experimental results.

EXAMPLE 1

In this example, an alumina-glass-based dielectric material was preparedas a material for a ceramic green sheet. A binder and organic solventwere mixed with the material to obtain a mixture, and the mixture wassubjected to the doctor blade method to produce a ceramic green sheethaving a thickness of 125 μm. On the other hand, atridymite-silica-based material was prepared as a material for shrinkagesuppression. Similarly to the ceramic green sheet material, a binder andorganic solvent were mixed with the material to obtain a mixture, andthe mixture was subjected to the doctor blade method to produce ashrinkage suppression green sheet having a thickness of 125 μm.

The ceramic green sheet was formed with a first square through holehaving a side of 4 mm using a die. On the other hand, the shrinkagesuppression green sheet was similarly punched out using a die to form afirst fitting sheet of a square having a side of 4 mm. The first fittingsheet was fitted in the first through hole to produce a first compositegreen sheet. The first composite green sheet had a thickness of 125 μm.Subsequently, a ceramic green sheet is punched out using a die to form acavity, and the punched-out portion was set in position in the cavity toproduce a cut formation sheet. Six cut formation sheets were prepared.Furthermore, a shrinkage suppression green sheet was formed with a sixththrough hole of a square having a side of 4 mm using a die. A ceramicgreen sheet was punched out to form a second fitting sheet of a squarehaving a side of 4 mm. The second fitting sheet was fitted in the sixththrough hole to produce an uppermost composite green sheet. Thethickness of each cut formation sheet was set to be 125 μm.

One shrinkage green sheet constituting a lowermost layer, five ceramicgreen sheets, one first green sheet, four cut formation sheets and oneuppermost composite green sheet were laminated in the order mentioned toform a multilayer body. The multilayer body placed in an ordinary diehaving upper and lower flat punches was pressed under a pressure of 70MPa for 7 minutes and then fired at 900° C.

After the firing step, the sheets inside the cavity protruded from thesurface of the fired multilayer body. When the inside sheets wereallowed to exfoliate spontaneously, though residuals were attached tothe corners of the cavity and could be caused to fall off through theultrasonic cleaning in an organic solvent. The shrinkage suppressiongreen sheet and uppermost composite sheet could also be caused to falloff.

The multilayer ceramic substrate thus obtained was 0.59 mm in thickness,and the cavity had a one side of 4 mm at the opening and a depth of 0.30mm. A photograph showing the cross section of the multilayer is shown inFIG. 74 from which it is found that the cavity has a shape of a drumhaving a larger opening area at the inside than at the opening.

EXAMPLE 2

In this example, a multilayer ceramic substrate having a multistagecavity was fabricated. The production method set forth in the secondembodiment was used herein. The ceramic green sheet and shrinkage greensheet were formed pursuant to Example 1.

In the multilayer ceramic substrate, the first cavity portion had a sideof 5 mm at the opening and a depth of 0.24 mm, and the second cavityportion had a side of 2 mm at the opening and a depth of 0.18 mm. Aphotograph showing the cross section of the multilayer is shown in FIG.74 from which it is found that each of the cavity portions has a shapeof a drum having a larger opening area at the inside than at theopening.

EXAMPLE 3

In this example, an alumina-glass-based dielectric material was preparedas a ceramic material for a substrate and mixed with an organic binderand organic solvent to obtain a mixture. The mixture was subjected tothe doctor blade method to produce a ceramic green sheet having athickness of 125 μm

On the other hand, a tridymite-silica-based material was prepared as amaterial for shrinkage suppression and mixed with an organic binder andorganic solvent similarly to the ceramic material to obtain a mixture.The mixture was subjected to the doctor blade method to produceshrinkage suppression green sheets having a thickness of 110 μm and athickness of 125 μm, respectively. As a burnable material, theaforementioned ceramic material for the substrate and the resin usedwhen the shrinkage suppression material was formed into a sheet wereprepared. The burnable material was dissolved in an organic solvent andthe resultant was subjected to the doctor blade method to produce aburnable sheet having a thickness of 15 μm.

A ceramic green sheet was punched out using a die to form a squarecavity portion having a side of 2 mm. On the other hand, the shrinkagesuppression green sheet having a thickness of 110 μm and burnable sheetwere punched out to obtain a square shrinkage suppression green sheetpiece and square burnable sheet piece each having a side of 2 mm. Thesepieces were fitted in the cavity portion to produce a composite greensheet for a cavity bottom.

Another ceramic green sheet was punched out to form a square cavityportion having a side of 2 mm, and the punched-out portion was fitted inthe cavity portion to form a ceramic green sheet for cavity formation.Six cavity formation ceramic green sheets were prepared.

Furthermore, the shrinkage suppression green sheet having a thickness of125 μm was punched out using a die to form a square cavity portion inwhich a ceramic green sheet piece was fitted to form an uppermostcomposite green sheet.

o non-processed ceramic green sheets, one of which constituted a cavitybottom were laminated, on which six cavity formation ceramic greensheets were laminated, followed by lamination of an uppermost compositegreen sheet. A non-processed shrinkage suppression green sheet 125 μm inthickness was used as the lowermost sheet. The cross section of thecavity portion of the multilayer body thus formed is as shown in FIG.18( a).

The multilayer body thus obtained was placed in an ordinary die havingupper and lower flat punches, pressed under a pressure of 700 kg/cm² forseven minutes and then fired 900° C. The fired ceramic substrate was notshrunk in the in-plane direction, but greatly shrunk only in the widthdirection. Since the multilayer was shrunk in the in-plane direction atthe cavity portion, the shrinkage in the thickness direction was smalland, therefore, the upper part of the cavity portion protruded from thesubstrate surface.

Though the tridymite-silica-based shrinkage suppression materialexfoliated spontaneously from the fired ceramic substrate, sinceresiduals were attached to the corners of the cavity inside, the firedceramic substrate was subjected to ultrasonic cleaning in an organicsolvent. Thus, a multilayer ceramic substrate having a square cavitythat had one side of 2 mm at the opening and a depth of 0.42 mm andhaving an entire thickness of 0.55 mm was obtained. In the multilayersubstrate, the cavity bottom was flat sufficient for mounting anelectronic device thereon.

1. A production method of a multilayer ceramic substrate having acavity, comprising the steps of: laminating a plurality of substrategreen sheets including cavity formation green sheets having throughholes corresponding to the cavity to form a multilayer body; laminatinga shrinkage suppression green sheet piece on one of the plurality ofsubstrate green sheets constituting a bottom of the cavity; disposingembedded green sheets separated from the cavity formation green sheetson the shrinkage suppression green sheets piece in the cavity; forminganother though hole in an upper shrinkage suppression green sheetcorresponding to a shape of an opening of the cavity, and fitting anembedded green sheet in the another through hole; laminating the uppershrinkage suppression green sheet with the embedded green sheet thereinon an upper surface of the substrate green sheets so that the embeddedgreen sheet in the upper shrinkage suppression green sheet is located onthe embedded green sheets in the cavity, and a lower shrinkagesuppression greet sheet under a lower surface of the substrate greensheets, respectively, which surfaces constitute outermost layers of themultilayer body; pressing the multilayer body; firing the pressedmultilayer body so that the embedded green sheets in the cavity shrinkand separate from the cavity formation green sheet; and, removing thefired embedded green sheets.
 2. A production method of a multilayerceramic substrate according to claim 1, wherein the cavity formationgreen sheet laminated immediately on the substrate green sheetconstituting the bottom of the cavity is formed with a through hole inwhich the shrinkage suppression green sheet piece is fitted.
 3. Aproduction method of a multilayer ceramic substrate according to claim2, wherein the shrinkage suppression green sheet piece has a thicknesssubstantially identical with that of the substrate green sheet.
 4. Aproduction method of a multilayer ceramic substrate according to claim1, wherein the cavity has an opening and a multistage shape having anopening dimension decreasing stepwise in a direction of depth of thecavity to form cavity portions having bottoms, and further comprisingthe step of disposing on each of the bottoms of the cavity portions ashrinkage suppression green sheet piece.
 5. A production method of amultilayer ceramic substrate according to claim 1, further comprisingthe step of interposing a burnable sheet between the shrinkagesuppression green piece and the embedded green sheet.
 6. A productionmethod of a multilayer ceramic substrate according to claim 5, whereinthe cavity formation green sheet laminated immediately on the substrategreen sheet constituting the bottom of the cavity is formed with athrough hole in which the shrinkage suppression green sheet piece and aburnable sheet are fitted.
 7. A production method of a multilayerceramic substrate according to claim 6, wherein the shrinkagesuppression green sheet piece and the burnable sheet have a totalthickness substantially identical to that of the substrate green sheet.8. A production method of a multilayer ceramic substrate according toclaim 5, wherein the cavity has an opening and a multistage shape havingan opening dimension decreasing stepwise in a direction of depth of thecavity to form cavity portions having bottoms, and further comprisingthe step of disposing on each of the bottoms of the cavity portions ashrinkage suppression green sheet piece and a burnable sheet.
 9. Aproduction method of a multilayer ceramic substrate according to claim5, wherein the burnable sheet is formed of a resin material.
 10. Aproduction method of a multilayer ceramic substrate according to claim9, wherein the resin material is identical with that contained in thecavity formation green sheets.
 11. A production method of a multilayerceramic substrate according to claim 1, further comprising the step ofinserting cuts corresponding to a shape of the cavity in the cavityformation green sheets to separate cut portions therefrom and using theseparated portions as the embedded green sheet.
 12. A production methodof a multilayer ceramic substrate according to claim 1, wherein thecavity formation green sheet is formed with a through hole correspondingto a shape of the cavity, and the embedded green sheet formed bypunching out separately is fitted in the through hole.
 13. A productionmethod of a multilayer ceramic substrate according to claim 1, whereinthe shrinkage suppressing green sheet pieces on a portion of the cavityare amended in thickness.
 14. A production method of a multilayerceramic substrate according to claim 13, wherein a cavity formationgreen sheet laminated immediately on the substrate green sheetconstituting the bottom of the cavity has a thickness different fromthose of other cavity formation green sheets, and the thickness of theshrinkage suppressing green sheet pieces is set different from thethickness of the cavity formation green sheet.
 15. A production methodof a multilayer ceramic substrate according to claim 13, wherein ashrinkage suppression green sheet disposed on a surface of an outermostsubstrate green sheet on a side opposed to a side of an opening of thecavity is set to have a part facing the cavity and other part ofdifferent thickness.
 16. A production method of a multilayer ceramicsubstrate according to claim 15, wherein the shrinkage suppression greensheet comprises a laminate of a first shrinkage suppression green sheethaving a prescribed thickness and a second shrinkage suppression greensheet formed at the part facing the cavity with a through hole.
 17. Aproduction method of a multilayer ceramic substrate according to claim1, further comprising the steps of forming a conductive pattern on thesubstrate green sheet constituting the bottom of the cavity asstraddling a periphery of the cavity bottom, forming a first cavityformation green sheet having a through hole in which a shrinkagesuppression green sheet piece is embedded and a second cavity formationgreen sheet laminated immediately on the first cavity formation greensheet and having an embedded green sheet that is separate from thecavity formation green sheet embedded in the cavity, laminating thefirst and second cavity formation green sheets, respectively,immediately on the substrate formation green sheet constituting thebottom of the cavity and immediately on the first cavity formation greensheet so that the cavity bottom, the shrinkage suppression green sheetpiece and the embedded green sheet overlap to form the multilayer, inwhich the shrinkage suppression green sheet piece in at least a portionof the periphery of the cavity bottom overlapping the conductive patternhas an end face disposed outside an end face of the embedded green sheetthe second cavity formation green sheet has.
 18. A production method ofa multilayer ceramic substrate according to claim 17, wherein theshrinkage suppression green sheet has a size larger than that of theembedded green sheet.
 19. A production method of a multilayer ceramicsubstrate according to claim 18, wherein the end face of the shrinkagesuppression green sheet piece is disposed outside the end face of theembedded green sheet over the entire periphery of the cavity bottom. 20.A production method of a multilayer ceramic substrate according to claim17, wherein the shrinkage suppression green sheet piece and the embeddedgreen sheet have a same shape and are laminated so that the two are outof alignment to partially overlap each other.
 21. A production method ofa multilayer ceramic substrate according to claim 17, wherein the endface of the shrinkage suppression green sheet piece in at least theportion of the periphery of the cavity bottom overlapping the conductivepattern and the end face of the embedded green sheet in at least aportion the shrinkage suppression green sheet piece and the end face ofthe embedded green sheet have a distance of 0.1 mm to 0.5 mmtherebetween.
 22. A production method of a multilayer ceramic substrateaccording to claim 17, wherein the shrinkage suppression green sheetpiece is fitted in the through hole of the first cavity formation greensheet.
 23. A production method of a multilayer ceramic substrateaccording to claim 22, wherein the shrinkage suppression green sheetpiece has a thickness substantially identical with that of the firstcavity forming green sheet.
 24. A production method of a multilayerceramic substrate according to claim 17, wherein the cavity has anopening and a multistage shape having an opening dimension decreasingstepwise in a direction of depth of the cavity to form cavity portionshaving bottoms, and further comprising the step of disposing on each ofthe bottoms of the cavity portions a shrinkage suppression green sheetpiece.
 25. A production method of a multilayer ceramic substrateaccording to claim 24, wherein when disposing on each of the bottoms ofthe cavity portions a shrinkage suppression green sheet piece, in atleast the portion of the periphery of the cavity bottom overlapping theconductive pattern, the end face of the shrinkage suppression greensheet piece is disposed outside the end face of the embedded green sheetlaminated immediately on the shrinkage suppression green sheet piece.26. A production method of a multilayer ceramic substrate according toclaim 17, further comprising the step of causing a burnable sheetintervening between the shrinkage suppression green sheet piece and theembedded green sheet.
 27. A production method of a multilayer ceramicsubstrate according to claim 26, wherein the second cavity formationgreen sheet is formed with a through hole corresponding to a shape ofthe embedded green sheet in which the shrinkage suppression green sheetpiece and a burnable sheet are fitted.
 28. A production method of amultilayer ceramic substrate according to claim 27, wherein thesubstrate green sheet and the burnable green sheet have a totalthickness set substantially identical with that of the second cavityformation green sheet.
 29. A production method of a multilayer ceramicsubstrate according to claim 1, further comprising the steps of forminga conductive pattern on the substrate green sheet constituting thebottom of the cavity as straddling a periphery of the cavity bottom anda softening layer that gets soft at a firing temperature of the firingand is provided at least on a surface of the conductive pattern of aportion corresponding to the periphery of the bottom on the cavitybottom formation ceramic layer, before the pressing step, laminating thecavity formation green sheet having the shrinkage suppression greensheet embedded in the through hole immediately on the substrateformation green sheet constituting the cavity bottom so that the cavitybottom and the shrinkage suppression green sheet piece overlap andlaminating a cavity formation green sheet so that the embedded greensheet separate from each cavity formation green sheet as being filled inthe cavity is disposed on the shrinkage suppressing green sheet pieceand, after the firing step, removing the embedded green sheet fired. 30.A production method of a multilayer ceramic substrate according to claim29, wherein the softening layer is provided entirely of the periphery ofthe bottom.
 31. A production method of a multilayer ceramic substrateaccording to claim 29, wherein the periphery of the bottom and an outerperiphery of the softening layer have a distance of 0.1 mm to 0.5 mmtherebetween.
 32. A production method of a multilayer ceramic substrateaccording to claim 29, wherein the periphery of the bottom and an innerperiphery of the softening layer have a distance of 0.5 mm or lesstherebetween.
 33. A production method of a multilayer ceramic substrateaccording to claim 29, wherein the softening layer is formed of glass.34. A production method of a multilayer ceramic substrate according toclaim 33, wherein the glass is the same as that contained in thesubstrate green sheet.
 35. A production method of a multilayer ceramicsubstrate according to claim 29, wherein the shrinkage suppression greensheet piece is fitted in a through hole of the cavity formation greensheet laminated immediately on the bottom formation green sheet.
 36. Aproduction method of a multilayer ceramic substrate according to claim35, wherein the shrinkage suppression green sheet piece has a thicknesssubstantially identical with that of the substrate green sheet.
 37. Aproduction method of a multilayer ceramic substrate according to claim29, wherein the cavity has an opening and a multistage shape having anopening dimension decreasing stepwise in a direction of depth of thecavity to form cavity portions having bottoms, and further comprisingthe step of disposing on each of the bottoms of the cavity portions ashrinkage suppression green sheet piece.
 38. A production method of amultilayer ceramic substrate according to claim 37, wherein whendisposing on each of the bottoms of the cavity portions a shrinkagesuppression green sheet piece, in bottoms of the bottoms on which theconductive pattern is disposed as straddling a periphery of a bottom,the softening layer is formed on a surface of at least the conductivepattern of portions corresponding to the periphery on the bottomformation green sheet constituting the bottom.
 39. A production methodof a multilayer ceramic substrate according to claim 29, furthercomprising the step of interposing a burnable sheet between theshrinkage suppression green piece and the embedded green sheet.
 40. Aproduction method of a multilayer ceramic substrate according to claim39, wherein the cavity formation green sheet laminated immediately onthe bottom formation green sheet is formed with a through holecorresponding to a shape of the cavity, and the shrinkage suppressiongreen sheet piece and a burnable sheet are fitted in the through hole.41. A production method of a multilayer ceramic substrate according toclaim 40, wherein the shrinkage suppression green sheet piece and theburnable sheet have a total thickness substantially identical to that ofthe cavity formation green sheet.
 42. A production method of amultilayer ceramic substrate according to claim 1, wherein the shrinkagesuppression green sheet and the shrinkage suppression green sheet piececontain as a shrinkage suppression material at least one speciesselected from the group consisting of quartz, cristobalite andtridymite.
 43. A production method of a multilayer ceramic substrateaccording to claim 42, wherein the shrinkage suppression green sheet andthe shrinkage suppression green sheet piece are formed of a compositioncontaining tridymite and an oxide difficult to sinter.
 44. A productionmethod of a multilayer ceramic substrate according to claim 1, whereinthe step of firing is performed at a temperature of 800° C. to 1000° C.45. A production method of a multilayer ceramic substrate according toclaim 1, further comprising the step of cleaning residuals after thestep of firing.
 46. A production method of a multilayer ceramicsubstrate according to claim 45, wherein the step of cleaning comprisesultrasonic cleaning in a solvent.
 47. A production method of amultilayer ceramic substrate according to claim 45, wherein the step ofcleaning comprises wet blasting.
 48. A production method of a multilayerceramic substrate according to claim 1, wherein upon firing the pressedbody, the embedded green sheets filled in the cavity formation greensheets and the embedded green sheet in the upper shrinkage suppressiongreen sheet shrink and are separated from the cavity formation greensheets and the upper shrinkage suppression green sheet, respectively,and also, extend upwardly.